# Hackaday Dictionary: Mils and Inches and Meters (oh my)

Measuring length is a pain, and it’s all the fault of Imperial measurements. Certain industries have standardized around either Imperial or metric, which means that working on projects across multiple industries generally leads to at least one conversion. For everyone outside the last bastion of Imperial units, here’s a primer on how we do it in crazy-land.

## Definitions

The basic unit of length measurement in Imperial units is the inch. twelve inches make up one foot, three feet make up one yard, and 5,280 feet (or 1,760 yards) make up a mile. Easy to remember, right?

Ironically, an inch is defined in metric as 25.4 millimeters. You can do the rest of the math for exact lengths, but in general, three feet is just shy of a meter, and a mile is about a kilometer and a half. Generally in Imperial you’ll see lots of mixed units, like a person’s height is 6’2″ (that’s shorthand for six feet, two inches.) But it’s not consistent, it’s English; the only consistency is that it’s always breaking its own rules. You wouldn’t say three yards, two feet, and six inches; you’d say 11 1/2 feet. If it was three yards, one foot, and six inches, though, you’d say 3 1/2 yards. There’s no good rule for this other than try to use nice fractions as often as you can.

Users of Imperial units love fractions, especially when it comes to parts of an inch or mile. You’ll frequently find drill bits in fractions of an inch, which can be extremely frustrating when you are trying to do math in your head and figure out if a 17/64″ bit is bigger than a 1/4″ bit (hint, yes, it’s 1/64″ bigger).

If it wasn’t hard enough already, there came the thousandth of an inch. As the machine age was getting better and better, and parts were getting smaller and more precise, there came a need for more accurate measurements than 1/64 inch. Development of appropriate tools for measuring such fine resolution was critical as well. You can call a 1/8″ bit a .125″ bit, and that means 125 thousandths of an inch. People didn’t like to wrap their mouths around that whole word, though, so it was reduced to “thou.” Others used the latin root for thousand, “mil.” To summarize, a mil is the equivalent of a thou, which is one thousandth of an inch. It should not be confused with a millimeter. It takes about 40 mils to make 1 millimeter. Also, the plural of mil is mils, and the plural of thou is thou.

## Tools

Measuring length is done with a variety of tools, from GPS for long distances, to tape measures for feet/meters, and rulers for inches/centimeters. When it comes to very small measurements, the caliper is the tool of choice. This is the kind of tool that should be in everyone’s toolbox. Initially it started with the inside caliper and outside caliper, which were separate tools used to measure lengths. The Vernier caliper combined the two, added a depth meter and a couple other handy features, and gave machinists an all-around useful tool for measuring. Just like the slide rule, though, as soon as digital options became available, they took over. The digital caliper can usually switch modes between decimal inches, fractional inches, and metric.

Also, while slightly off topic, if you haven’t seen this video on getting the most out of your tape measure, it’s well worth a few minutes.

## Uses

Every industry has picked a different convention. Plastic sheets are usually measured in mils for thin stuff and millimeters or fractions of an inch for anything greater than 1/32″. Circuit boards combine units in every way imaginable, sometimes combining mils for trace width and metric for board dimensions, with the thickness of the copper expressed in ounces. (That’s not even a unit of length! It represents the amount of copper in one square foot of area and 1 oz is equivalent to 1.4mil.) Most of the time products designed outside of the U.S. are in metric units, while U.S. products are designed in either. When combining different industries, though, the difference in standards gets really annoying. For example, order 1/8″ plexiglass, and you may get 3mm plexiglass instead. Sure the difference is only .175mm (7 thou), but that difference can cause big problems for pieces that are press fit or when making finger joints on boxes, so it’s important that when sourcing components, you not only verify the unit, but if it’s a normal unit for that industry and it’s not just being rounded.

Often you can tell with what primary unit a product is designed with only a few measurements of a caliper. Find a dimension and see if it’s a nice round number in metric. If it’s not, switch it to imperial, and watch how quickly it snaps to a nice number.

## Moving forward

Use metric if you can. The vast majority of the world does it. When you are sending designs overseas for production they will convert to metric (though they are used to working in both). It does take time to get used to it (especially when you are dealing with thou/mils), but your temporary discomfort will turn to relief when your design doesn’t crash into the Mars (or more realistically when you don’t have to pull out the Dremel and blade to get your parts to fit together).

## 197 thoughts on “Hackaday Dictionary: Mils and Inches and Meters (oh my)”

1. Ed Seery says:

Thats 25.4 not 24.5

2. David says:

Also be aware that when a US machinist says “tenths” he usually meams ten-thousandths (0.0001) of an inch.

3. I used to be a mechanical engineer (on the East coast of the US if that makes any difference) and I don’t remember ever hearing someone use “thou” for thousandths of an inch. I always used “thousandths” and, to add another word, “tenths” for ten thousandths of an inch. As in: “This shaft doesn’t fit in this bearing, grind 2 tenths off the diameter” Or “It isn’t a critical dimension, plus or minus 10 thousandths is good enough”

1. Bashh says:

As a mechanical engineer also on the east coast of the US, I can say we use the word thou all the time at my place of business.

2. t-bone says:

You’d have to be in a particular area of mechanical engineering. I’d never heard the terms, either, until I went to school for machining thirty years after college. I still can’t bring myself to use “thou”, though.

3. t-bone says:

Are we being hypocrites for not having this discussion in Esperanto?

1. Michael says:

No we just need to convert to dozenal (base 12) so that to convert cm to m you need to multiply by 84 so that nobody is happy.

4. As a British mechanical engineer, ‘Thou’ is commonly used when talking about thousandths of an inch. Maybe it’s a British thing?
Any if you US guys think you have it bad having to use imperial, try the odd job mix of imperial and metric we have! You buy milk in pints but juice in litres, you weigh yourself in Stone and Lbs at home but kg at the gym, most distances are metric except for when driving then it’s miles, most engineering is done in mm except pipes and hydraulics which seem to use imperial!

1. enl says:

Oy! Don’t talk of piping. One, and only one, full line supplier on the east coast for metric (DIN, etc) fittings. The pipe sizes are the same, metric being really inch size nominal referenced as nearest size in mm (3/4″ pipe is 20mm or 19mm, depending on the print and country of origin, but is within tolerance for OD of 3/4 nominal in the US either way, though JIS is just at the top end and fitting JIS pipe into din or ASTM/ASME fittings can on occasion require a bit of work), and the threading is the same in most cases, flanges are the rule in the wild in industry, and the metric word makes the imperial world look logical. JIS, DIN, and all of the rest are TOTALLY incompatible with each other, as well as incompatible with US standards.

I feel for you.

On the other hand, I pointed out to one of our planners that a metric ton and a long ton are, substantially, the same, with a long ton ever so slightly greater, and he started bidding using long tons. Most clients, where this is an issue, work with either standard or long ton if they are imperial, and the rest work metric, so as long as it is a clear spec for long ton, things work out.

2. MoJo says:

Has to be thou, because “mil” means “millimeter” so there would be too much confusion. In the UK engineers tend to use metric, it’s only really trades people who still use Imperial measures.

3. phuzz says:

Just this weekend, I was cutting pieces of wood to 79cm long, and then screwing it in six inches apart.
Generally I’ll use metric (or more likely, SI units), because it makes the maths easier, but if I measure something and it’s exactly 6″, I’ll stick with that rather than dealing with 15.25cm.

1. phuzz says:

Oh, and there’s our road signs that are usually in miles, but use meters for short distances.
Brits end up being good at both imperial and metric, and we tend to use whatever’s easiest at the time.

4. Alex99a says:

Boy, that’s a lousy cheap low-quality socket wrench set. I should know, I have one just like it. :)

1. I love how metric socket sets have 1/4″ or 3/8″ square drives. Perhaps it’s different in Europe and Asia, but in North America there’s no such thing as a metric ratchet.

1. James Burke says:

Nope it’s the same in the UK at least, 1/4″ 3/8″ 1/2″ ratchets onto metric sockets, only reason I can think of is that a ratchet is a ratchet, no need for metric or imperial as it doesn’t matter and by keeping it that way all sockets will fit.

1. fascinating story about sprockets. the Metric equivalent is used by nobody. Turned out to be created by standards committee with no understanding of when things break. Whereas the imperial sprocket sizes are based on real world uses. so it’s one of the SI that never gets used.

1. Exactly. That’s the thing about metric “fanboys” (& girls). Assuming a unit is easier to work with because you “simply” move the decimal point is… kind of missing the point. The reason there are so many different units is because different fields need a convenient unit FOR THEIR FIELD, not because of stubbornness or even geography. This is why older units are persistent too. Yea sometimes a metric unit might be convenient enough here and there, but powers of 10 are very often not useful, but rather being able to divide by half, thirds, fourths etc. is very useful in many fields, and in metric there’s 5 and 2 and then you’re already into fractions, which apparently the original author struggles with I guess. Sounds a little like cognitive dissonance to me.
Anyway, when you’re dealing with a particular field and the only way to divide your stuff up gets you into 1/10 of your useful range so abruptly, it can quickly become nonsensical to experts in that field.
The fact that a unit is so unpalatable to large groups of people that governmental imposition and enforcement is the only way to make it happen seems to me to be reason to look deeper into the matter. How is it that bureaucrats who very possibly suck at math in the first place feel that they know best what unit any particular field should be using? Seems at least a little arrogant to me.

2. bzyzny says:

@vinito64

If your field benefits from using fractions, no one is stopping you from using metric fractions. For example, 2/3cm or 23/64mm, 1/80m, etc. The inconvenience of imperial units is inconsistency like 3ft to a yard but 12 inch to a foot.

2. Jii says:

It is the same in Europe.

1. And plumbing fixtures too. You can buy a 3/8″ to 1/2″ adapter to go with your 9mm ID faucet hoses. The mind boggles.

1. And car rims (17″) and monitor diagonals (27″) and… Europeans claim to be metric.

2. Jii says:

Yeah, there are things that are just legacy and not really worth the effort to change.

3. Dax says:

” and monitor diagonals (27″) and… Europeans claim to be metric.”

The French measure monitors and televisions in cm. It’s printed on the box across continental Europe, but the adverts are all in inches anyways because that’s the way it’s been done since forever.

4. It’s kinda sad this hasn’t changed much in the last decades.
But since ~2010 there is a ‘law’ (at least in germany) which forces businesses to use “gesetzlicher Einheiten” (legal units -> metric units) in inter business affairs and advertising.
They can still use ‘other’ units as a secondary, but if they don’t want to get sued by competitors they have to use metric units as the primary.

5. Whatnot says:

Monitor sizes are set by the asians not the europeans.

And they actually have millimeter on some sites, but it’s z times y rather than the diagonal.
On TV’s they use inches and centimeters both, but most often inches

6. fonz says:

and 3/8″ or 1/2″ thread a nowhere near 3/8″ or 1/2″ in size

3. John says:

Nah, we use 6.35 mm and 9.525 mm drives. :)

1. notarealemail says:

+1
*continous laughter*

1. RÖB says:

I like asking for imperial sheets at the hardware store. They tell me that they only have metric so I ask them to trim a sheet to imperial dimensions for me. When they measure their 6′ x 4′ sheets they find that their actually 1219 x 1829mm instead of 1200 x 1800 or in other words they ARE 6′ x 4′ to start with.

2. As an aside, in the auto industry you could pretty much count on any bolt or nut being either 9/16″ or 1/2″ – you could do pretty much all the work needed with just those two wrenches. When they went to Metric they didn’t settle on 12mm and 14mm or 10mm and 13mm or anything like that, they use every size available and you really do need a full set of wrenches.

1. Jii says:

13mm and 10mm are the wrenches used the most. They are always lost :)

1. notarealemail says:

That is so true! :D

2. Lennart says:

I have four 13mm, right now.
It is by the simple rule: if you can’t find a thing, buy a new and you find the old one…

3. fonz says:

10mm and 13mm is M6 and M8 that goes a long way

4. Tom says:

That’s why I have a wrench with 10mm at one side and 13mm on the other (as most Dutch rowers do), so I can loose both at the same time :)

2. Jonny says:

Eh, Toyotas are made of 10mm everything though

3. == says:

ive noticed a similar problem working on my truck.
metric body. inch engine.
13mm > 1/2″ > 12mm

True, I have to replace the rear brakes and front wheel bearings on my 06 Mazda now.
14mm on the rear brakes, 17mm on the front brakes, tie rods and upper control arms, 23mm on the lower control arms and best of all, 34mm axle nut. Idk what idiot at Mazda came up with using that size axle nuts. 34mm sockets are pretty much unobtainium at the local hardware stores and not even the local garages have them.

5. I was absolutely gob-smacked when I went to work for Boeing in 1980 and discovered their jets are designed and built in feet and inches, not meters. Holdover from the 707 era. I’ll bet the 787 is English not Metric, too.

1. And the English REALLY hate it when you call them “English” units, ‘cos apart from pints of beer and miles of road, England went pretty damned metric aaaaaaaages ago.

1. FredTheRanger says:

except people know their weight in stones… whatever that is.

1. 14lb, but only strange people still use stones, pounds, or ounces these days. This may include drug dealers selling in “eighths” and “teenths”.

1. Greenaum says:

Ketamine’s in grams, and you can buy marijuana in grams too, depends how much you want. Been a while, so I’ve no idea what it costs now. Heroin’s supposed to be 0.2g, generally though is more like 0.15g.

2. I would say that weights in Stone and Pound are probably the most common in use over here in the UK! Although it seems recently that more people are starting to use kg.

2. macona says:

I worked at a machine shop that did contract work for Boeing on 777 parts, among other things. Everything is in inches. And why not, everything is machined on CNC. Either unit is arbritary. Plus all the guys have imperial measuring tools so it is easier to do QC.

1. it’s like they are speaking in tongues…

6. Chamo says:

I truly hate imperial units…

1. Moryc says:

Star Trek is better than Star Wars – they use metric system…

1. Greenaum says:

Ah yes but Star Wars was a long time ago. They didn’t have Metric then.

1. Just don’t mention parsecs as a time unit :-D

2. Greenaum says:

I wasn’t going to!

3. travelling at light speed is constant so parsecs can be used as a measurement of time. That’s what they taught me at flight school anyway.

4. Greenaum says:

They taught you parsecs at the speed of light at flight school? What planet was this school on?

Actually in the film parsecs were used as a unit of time, to demonstrate speed, how fast Han was going on his Kessel Run. So that sounds a bit off, there’s some redundancy in there somewhere, if that was the case. But it isn’t the case, they just got it wrong.

There’s other mad, overly complicated fan-theories involving defining the Kessel Run as some more complicated things. My theory, though, is that a wizard did it.

1. notarealemail says:

I love tvtropes!
*new tab* *new tab* *new tab* *new tab* *new tab*

2. Chamo says:

Fantastic! Thanks.

1. RoboMonkey says:

“Once again the inch will rule the galaxy!”

7. weirdwhit says:

I sell a brand of motorized shades at my 9 to 5. One of their factory sales reps loves to use the term “millimeters of a second” to describe how quickly the shades react to commands. At first I thought it was just a one time slip up, but i’ve heard him say it multiple times now and its driving me crazy. Do you even measure, bro?

1. “dude, you can… uh… um…abbreviate, yah, abbreviate millimeters per second as ‘milliseconds'”.

1. Marc T says:

I am no scientist but surely milliseconds (scalar) is a measure of time and millimeters per second (vector) is a measure of velocity.

8. A 10x10x10 centimetre cube of water is 1 litre, and weighs 1 kilogram. 1x1x1cm of water is 1 millilitre and weighs 1 gram.
There are 100 centi-things or more normally 1000 milli-things in a thing, and 1000 things are a kilo-thing. Everything is in 10s

1 cubic inch of water, on the other hand, has a volume of,err, 0.55411255 fluid ounces(?), yet weighs 0.57814024 ounces, umm, OK one cubic foot of water is, err, 7.4805198 gallons, and weighs 62.42796 pounds, uh… OK one pound of water occupies… OK I give up.
… and there might be 3, 8, 12, 14, 16, 60, or 144 things in the next biggest thing up, err, or maybe 22, 80, what the ####ity ####?!?

1. pff says:

i don’t like ‘gauge’s
numbers go the wrong way. yes i understand the reason but it doesn’t make sense to say something has been resized 00 times.

2. notarealemail says:

Question: Does the measurement system for ‘tyres’ use mixed units like it does in the US, or is it always in metric?

1. Jii says:

Mixed, rim size in inches, width in mm, profile in percent.

2. nraynaud says:

for bikes in Europe there is a delightful confusion on rim sizes with most of them in inches, but there is a 700mm size too.

1. GuW says:

All tyre sizes in Europe is in mm.

There is 26″ 27½” and 29″ mountanbike tyres that are 559, 584 an 622mm

But then again we used to use 26″ way back that was 584mm, and a 28″ that was 635m

Of the top of my head there is

559mm=26″
584mm=26″ or 27½”
590mm=26″
609mm=27
622mm=28″ or 29″
630mm=27″
635mm=28″
642mm=28″

And then there is like 3 different 22″, 2 different 24″ and so on.

The “european 700size” vyou refer to is just the french way to say 622mm, you know the french, official holder of the meter? They just invented their own measuring system for fun….

1. MrFluffy says:

All the tyres I see are in inches still on diameter, or puces as they are known here in France…
Rim widths are a different kettle of fish, most have gone metric on width and kept imperial diameters on the sidewall markings.

2. MrFluffy says:

pouces even, tyres generally dont suffer with fleas…

3. Galane says:

In the 1980’s there was a push to change car wheel diameters to metric. It didn’t stick, not even in the most die hard metric countries. https://en.wikipedia.org/wiki/Michelin_TRX IIRC in the USA only the Ford Escort EXP and perhaps the Merkur XR4Ti (Scorpio everywhere else, minus the uglification package and no option for 5.0 V8) got stuck with those odd size wheels that only hard to get and expensive tires were available for.

Many were the classified ads for used Escorts with bald TRX tires. :P “Crap! New tires cost more than my car is worth!”

Tire sizes here are like: 215/45 R17, which means:
215mm width, sidewall height 45% of width, radial, 17″ rim size
Afaik that system is pretty much universal

3. enl says:

Weighs 0.57814024 of WHICH ounces?

You missed the easy way, the one that makes it simple: one gallon is 231 cubic inches (standard US commercial gallon. YMMV if you use one of the several tens of other gallons…)

Also note that the international inch is defined as 25.4mm, which replaced the prior US legal inch which was defined as 39.37 inches == 1metre. Yup, they are different, and the old one is still used. in particular by surveyors, as old surveys use the definition of the foot based on it, unless they are really old and use a different foot, or are done in some other unit, like one of the various chains. My property map is in chains and links and fractions of a link. No the same ones as my neighbors, though. Mine are in 10 chain/furlong chains, I don’t recall what my neighbors (and most of the other properties in the are) is. Maybe 100ft chains?

The different inches show up, barely, when you are working with old precision tools or old precision equipment (pre 1960ish) built to inch rather than metre. Roughly 2ppm, which is approximately 2mm/km. I have never had it make a difference in any thing I do (the uncertainty on my gage blocks is a little larger than this, and the actual calibration includes roughly this magnitude error), but it matters a lot in some fields.

4. In the old fire extinguisher market (pre 2000) 1 gallon = 5.5 litres.

5. Michael says:

That is only true of pure water at 4 degrees.
How much does a deciliter of gold mass at 1075 degrees?
There is no logical reason why you can’t use kiloinches :p

6. Slartibart says:

Here’s a map for you so you don’t get lost:

Or wait, you WILL get lost with that map. Oh well.

You also got to love the ounce that is both a weight and a volume, or how they managed to mess up the ton with the short ton (2000lb), the long ton (2240lb), the metric ton (1000Kg) and the freight ton (which is a volume!). Also, where I live, a mile is 10km, just to cause some more confusion.

1. And that “helpful” map is ONLY LENGTH, no volumes or weights or anything.
As for your tons, are you absolutely sure they’re all tons and not tonnes? :-D

A nautic mile is both 6000 and 6080 feet! Using arc seconds is so much more convenient :)

3. TRN says:

The long and short tons are a legacy of cargo loading, load to the long deliver to the short, the difference would fall off or similar in transit. Also why the standard unit is a 44 gallon barrel of oil despite 55 gallon drums being common for storing oil. Units have a lot of legacy stuff, it’s rather like computers and bytes(there are ten bit bytes) and words, units depended on the use and cruft happened, and now common units are confusing if you look at all the definitions.

Metric isn’t immune either, it’s changed from a golden standard meter stick, to light waves in a time frame, and from a golden gram to spheres of silicon, and a with them, all the units defined only by those units have changed. Metric is fairly new all told, and still changing. Heck, the most correct clocks mean are least useful, as moving them throws them off.

Imperial work satisfactorily, yes, it has problems, but it works.
PS. displacement is measured in tons, and that can be of fresh water, salt water, or air. Yet more fun.

1. I thought displacement was measured in cubic inches. :D

2. Greenaum says:

Platinum kilogram, technically. And defining metres as light waves is just making it more accurate, I doubt the difference is more than the margin of error in the old definition. And more importantly than ALL of that, is it’s based on ten! Just like our number system. That alone is a million more reasons for Metric over Imperial.

Sure Imperial works, except when it doesn’t. Are inches not the same on Mars? There’s many more opportunities to get things wrong, and it’s the opposite of intuitive. We’ve come a long way since Babylon, it’s about time we dropped their systems of measurement.

If I were American, I’d make some effort to bring in the Metric standard. Except a bunch of churches and right-wing politicians would try and make hay from opposing it.

4. that looks like one of the fun-maps/graphs from XKCD – not like something anyone should ever use in real life ;D

1. notarealemail says:

That was my first thought! Turns out it’s from Wikipedia…

2. oodain says:

and that itself should be enough of a reason to change.

5. Galane says:

How about HVAC capacity measured in tons. Tons of what?

1. Daniel says:

Over here tons are 1000kg and everyone knows that because that’s the unit used to talk about the weight of cars.
“With a class B driver’s license you may drive cars up to 3.5t”
“The round road sign with the 7,5t and the red ring means you may not pass if your vehicle weighs more than 7.5 tons”

1. RÖB says:

The ton / tonne has long been the measurement for trucks cars and loading for transport vehicles.

But 1000kg is the metric tonne. The imperial ton is a different weight but close to the tonne. They are not close enough to be interchangeable though.

6. Leonard says:

The map makes it more complex than needed. Drop cm, m, dam and hm – completely superfluous.

7. Roger Damm says:

US or UK Gallon

9. joe lowe says:

Maybe it’s the imperialist in me, but all the designs I upload to thingiverse use “standard” hardware. :-P

10. notarealemail says:

Here in the US water is sold in gallons, soda is in liters.

1. Wretch says:

Only the litre and 2-litre (soda) bottles. The smaller ones and cans are in ounces. (c:

1. notarealemail says:

Lol, that’s right!

I’m going to get a CUP of coffee now…

1. Jii says:

Do you mean the baking cup or any cup you can find in your cabinet?

1. Leithoa says:

Or the 64oz cup from the truck stop?

2. notarealemail says:

6 ounces in a styrene foam ‘8 oz cup’.

2. kominek says:

short, tall, grande or venti?

1. Greenaum says:

I think a holy war against Starbucks would be justified, at this point.

2. RÖB says:

ROFL @ [Greenaum]

3. Jonathan Wilson says:

Everyone knows Starbucks doesn’t sell coffee, they sell a liquid “almost, but not quite, entirely unlike coffee” :)

11. tekkieneet says:

I use mixed units for PCB. Imperial for the gird, track width/spacing because I can relate to those. Most of the higher density SMT footprints are specified in mm, so that eliminate mistakes/ accumulated round off errors. I use metric for drill sizes, dimensions, pitch for SMT parts, standoffs. This is because I can order cheap PCB from China and not have to worry about things rounded off/scaled wrong.

For most of the things, I can deal with either units. Temperature is another topic.

1. Moryc says:

I do everything related to PCB design in metric. This causes some odd number now and then, like 2,54mm pitch pf headers. I hate imperial units and refuse to use them. Everyone else should too…

1. absolutely!
Every time i read an article on HaD where the important numeric information are not in metric units, it makes me cringe.
IMHO HaD is a perfect place to propagate SI (not SI Units – that would a case of “… units units”) and this article surprises me because its message is in conflict with so many other articles on HaD.

1. rnjacobs says:

So why does “SI” get to not include the word “unit” directly in its acronym? Système international d’unités → SI, not SIU?

1. Ben says:

In Canada, we have to deal with this issue constantly. We have a large imperial neighbor, but all of our large engineering/ contracting firms use metric.
So to plan server rooms down to enclosures in metric, and fit things made and measured in imperial, means I have binders of conversion tables and shortcuts and a bottle of advil in my desk.

I also like spreading this quote around…
“In metric, one milliliter of water occupies one cubic centimeter, weighs one gram, and requires one calorie of energy to heat up by one degree centigrade—which is 1 percent of the difference between its freezing point and its boiling point. An amount of hydrogen weighing the same amount has exactly one mole of atoms in it.

Whereas in the American system, the answer to “How much energy does it take to boil a room-temperature gallon of water?” is “Go fuck yourself,” because you can’t directly relate any of those quantities.” -from Wild Thing: A Novel by Josh Bazell

2. enl says:

Fortunately in electronic design, most of the imperial units are simple decimal, and so convert to short, exact decimal fractions in SI, unlike the other direction, due to the difference between multiplying by 127/5 vs. 5/127 (It had to be a nontrivial prime denominator in decimal….)

I tend to use SI as much as I can, but I am roughly equally comfortable in either SI or Imperial. THere are a few things for which I have a distinct difference in comfort due to growing up in the ‘states back before the 1976 adoption of metric (1876? 1930something? How to keep them straight….) such as basic dimensions of a person (height, weight, waist size, etc) and application dependent use of heat units are cognitively locked on imperial for me. Combustion, enthalpys of fusion and vaporization of water, plant heating are all BTU and deg F. Pretty much everything else in thermo for me is SI.

3. tekkieneet says:

I just find the grid/track size easier as they are rounded integers in mils (1/1000″), so the design rules are easier to remember. I also have to work with PCB designers. It is easier to tell them to use 5/5 rules for single ended track and 6/4.5 for differentials etc. I supposed if I have to use metric, it would only take a couple of days to burn-in the new ones in my head. It is not a big deal for me.

Laser printers here are sold with DPI (dots per inch) for resolution. Back in the low res 300 DPI days, it was easier to know that my lines for my home made are integer multiples of the resolution. Now that’s not much of an issue.

I leave footprint native to whatever they were defined as. It makes it easy to just copy from the datasheet. I have seen some really messed up footprints that failed at math in unit conversions to imperial and wonder why all that stubbornness to one unit when the PCB can accept packages in both or even mixed units. (e.g. drill in metric while pitch in imperial).

12. TCB says:

Which is heavier, an ounce of gold or an ounce of feathers?

An ounce of feathers is heavier because gold is measured in ounces Troy.

Legacy units are super frustrating but we will not be free of them for ages.

1. Leithoa says:

…. Troy ounces are larger by ~10%

13. My biology teacher once told the class that Metric is more accurate than imperial. We argued up and down about that one. I’m not saying imperial is more accurate just different.

1. Greenaum says:

Not technically more “accurate”, literally furlongs and attometres are equally accurate, but in practice there’s much less potential for confusion.

1. Galane says:

There’s accuracy and there’s precision. 1,152 32nds of an inch in a 36 inch yard VS 1000 mm in a 100 centimeter (a bit over 39 inches) meter. Measuring in 32nds of an inch is more precise than measuring in millimeters but they’re both just as accurate – to the division used.

In the late 70’s there was a show on PBS to teach kids metric measuring. Problem was they were always using the word “about”. Whip out a metric tape measure to gauge a pizza and “It’s about 23 centimeters.” A building was about so many meters tall. Tall person? About two meters. How far to the next town? About 6 kilometers. Always just throwing down some gross rounding off instead of precisely measuring to the closest applicable division.

Then there’s the too large / too small unit issue. How tall is a person? 5′ 8″ Right, big units to get the major size then fine it down with a smaller unit. But elsewhere it’s 173 centimeters. What has the rest of the world got against the decimeter? I NEVER see it used. Why not 17 dm 3 cm? Here’s this handy middle of the road unit but nobody uses it. Most unit conversion software doesn’t have it. If you Google inch to centimeter, the drop list of other units does not have decimeter. If you Google for inch to decimeter, only then is it added to the list.
Degrees C are too damn large. There’s 180 degrees F between freezing and boiling water but only 100 degrees C. Fahrenheit is 80% more precise without having to go to sub-degree units.
How fast were you driving? 88! Oh, wait, that’s only 62 miles per hour. :P European car magazines, TV shows and manufacturers typically use 0 to 88 KM times because it’s the closest whole kilometer number to 60 MPH.

We just couldn’t easily relate to units that are so far off, high or low, from what we had always used. But those of us in grade school in the late 70’s did learn metric units as well as our normal ones, so we’re no totally clueless about SI.

We’re just fine with mixing units in a measurement instead of stating something in a larger number of a single type of smaller unit – except for the age of children under two years. Medical people insist on going by the number of months. Feh, should I ever have kids, when they get to six months I’m saying half a year old. At 12 months I’ll say “He’s the big one!”. Sixteen months? A year and a quarter.

As for writing dates, January 1, 2016 makes more sense to me than 1 January 2016. There are 12 months in a year, 365 or 366 days in a year and an infinity of years. Smallest quantity to largest. The other way goes by the size of each unit. A day is smaller than a month which is smaller than a year, but wait, “month” is a very imprecise unit with a size that varies between 28 or 29 and 31.

1. Hang on, dates, the US “middle-endian” is like “medium small large” and that makes MORE sense? The rest of the world is like “small medium large”, but BOTH are wrong and really we should all be using the ISO standard date format YYYY-MM-DD :-p

2. Dax says:

” What has the rest of the world got against the decimeter? I NEVER see it used. Why not 17 dm 3 cm? ”

It’s not easy to say. When someone asks “how tall”, you say “hundred and seventy three” and maybe add “cents”. Or you say “one seventy three”, or “meter seventy three”.

It creates confusion to say “seventeen and three” and so you have to add “seventeen decimeters and three centimeters” and then you’re into full tongue twister mode. You may be used to talking in two different units, but metric cultures aren’t. You pick one and you stick to it.

Decimeters aren’t used because they’re linguistically awkward. Deciliters are used because metric doesn’t have a “cup”.

“Degrees C are too damn large.”

For what? You can barely notice 1 C difference in room or water temperature with your hand.

1. Greenaum says:

Decilitres aren’t really used anywhere in the UK, I’ve never seen the word outside a maths book. You’d just say “half a litre” or “330mls” (if it’s a can of pop). I don’t think most people would know what a deci-anything is.

In practice Metric works in thousands, milligram, gram, kilogram. That’s enough, it’s no hardship saying “1 metre 73” over “17 decimetres and 3 centimetres”.

2. Even centimetres are kinda the odd-one-out here. Nobody uses centi-litres, centi-grams, centi-watts, or centi-anything-else except centimetres. The “correct” multipliers are almost always the powers of 1000, not 10s or 100s, so technically centimetres are an anomaly and we should all be using mm or m

3. Dax says:

Recently metrified countries don’t seem to “get” the deciliter because they seem to have invented their own “base 1000” rationale to the SI, but really they’re all meant to be used. Mills, cents, decis, they’re all perfectly useful units and used, except where it is taught that you should use only mm and m or only ml and liter – probably to make it easier for the teachers.

The metric system is designed to have more intermediate units around the 1 meter scale to give people a suitable unit to use for any particular task, and it goes to multipliers of 1000 for stuff that is either too small or too large to see and handle directly.

There’s milli, centi, desi, deka, hecto and kilo. 1/1000 – 1/100 – 1/10 – 10 – 100 – 1000 and beyond those the next multiplier is 1000. The only really odd one out is the deka because it’s more prone to confusion than simply saying “ten” – everything else is in common use. Even hectoliters are in use in e.g. brewing because barrels come in around that scale.

http://resolver.kb.nl/resolve?urn=urn:gvn:FSM01:2002-424&role=image&size=variable

14. The United States and Burma (I think) are the only countries that keep using the British units.
No even the British use the British units any longer.
Let that sink in for a while…

1. Leithoa says:

It’s the Republic of the Union of Myanmar now, get a new atlas.
Britain also drives on the left, still has a queen, and voted to leave the EU ( decision whose final ramifications remain to be seen).

I think the US and Myanmar will manage to function using ‘antiquated’ units just fine despite you not liking them.

15. Nyanman says:

Use metric because other people do so and because it will avoid you making a conversion error in cases that have been caused by people using both units.
Just because someone has a hard time with fraction and decimal doesn’t make one arbitrary system of length inferior to another. if anything, it’d be better to tell people to use what they are used to and not try and shift since THAT will cause more errors compared to actually using the system you know well.
The level of evangelization over metric and attempting to get everyone to use the ‘superior’ arbitrary measurement system because everyone uses it is honestly annoying. No need to go on and constantly remind people smugly that you’re using the better system because their system has (the horror) fractions that just don’t compute and they obviously need to convert to your system.

1. Whatnot says:

It’s not arbitrary, SI is the standard used in science and engineering by international agreement.
http://www.nist.gov/pml/wmd/metric/si-units.cfm
There’s your US government explaining things and the history, including that the US officially signed up to it.

2. dRudRudRu says:

+1 The biggest problem with using a measurement system that has fractions is that too many people can’t use fractions or never learned properly. When someone tells me “5/8”, I always hear “0.625” which is why I rarely have any issues using inches, mils, or millimeters as well as interchanging them. (which I have to do daily)

3. RÖB says:

Well ironically most of the people who visit HAD are stuck with at least some imperial even if their country is totally metric because the US tech industry spent so much time dragging it’s feet in converting.

Chip footprints like SOIC (1/20th of an inch) and SSOIC (1/40th of an inch) are still common place and in production. Most of the connectors in the PC you are using now (like AGP, PCI, PCIe) are also imperial.

One could argue that IBM was the most successful at getting computer technology into the consumer market. They did this by creating standards and many of those standards still exist today. Unfortunately IBM made these long term standards at a time when the US was imperial and most of the rest of the worlds was metric. Now we are still stuck with them.

The screws in my Acer desktop PC are imperial. Still !!!

1. Galane says:

ASCII = American Standard Code for Information Interchange. When created, there wasn’t much thought about interchange with anyone who wasn’t using English.

Thus the reason for double byte and Unicode and other methods of encoding languages with a superfluous amount of letters. ;)

Americans invented most of the technology the computing world is built upon, so everyone else adapted to it.

Quite unlike Television – we invented it then got stuck with pretty much the worst system for decades after others developed slightly higher resolution, but incompatible, analog TV systems. At least for HD everyone settled on 1920×1080.

1. Americans AND BRITS invented most of the technology the computing world is built upon, but apart from the hash vs pound thing, that doesn’t invalidate your argument much :-D

2. RÖB says:

1920 x 1080 is a problem, WXGA is 1920 x 1200, also some of the HDMI resolutions are just over a power of 2 boundary used for memory sizes so some resolution is dropped, so HDMI is already coming apart as a standard.

If you’re fluent in binary numbers, the imperial system makes a lot more sense :)

1. RÖB says:

0xFUCK

2. I agree, it’s surprising that Americans who work with 1/2, 1/4, 1/8, 1/16, 1/32, 1/64 on an almost daily basis when measuring stuff, aren’t wizards at using fractional math and binary arithmetic.

Maybe one day we’ll decide that that decimal system was a bad idea anyway (I think it would have made sense to use base-6 or base-11 if you think about it), and we’ll switch to hexadecimal which would also eliminate some problems with unrepresentable numbers (for example 1/10th in decimal is not representable as a binary fraction).

17. nraynaud says:

I grew up and live in the country that invented the meter and the kg, and I would like to point that we have a few inconsistencies over here too:
– the kg is a base unit, but it comes already with a prefix
– the kilo prefix is lowercase, while the normal rule is to have positive power prefix in uppercase, and diminutive prefixes in lowercase
– our mechanical drawings use mm by default and the architectural drawings use centimeter by default (the base unit is the meter)
– our use of unit of pressure is probably as “interesting” as the US use of units of length, the base unit is the Pascal, but every industry uses its own, up to the cm of water in some extreme cases. The atmospheric pressure is commonly told as “1015hP”, which respects zero rule for quantity formatting (either engineer formatting with an integer part between 1 and 999 and a multiple of 3 power prefix, or scientific formatting with an integral par between 1 and 9 and whatever unit prefix you can find)
– old people don’t understand Newtons and in particular N.m (and you never know if you should use 9.81 or 10 to do the conversion)
– units of area? the customary ones are a pain in the butt (the ones used in agriculture and for big properties)

1. Dax says:

“the kg is a base unit, but it comes already with a prefix”

That’s because the gram -used- to be the base unit, but it was found inconvenient because all the derived units became too small or too big, and therefore the lenght standard had to be changed to centimeters, to form the CGS system (centimeter-gram-second) that was supplanted by MKS or meter kilo second system which we use today.

The older system had all sorts of weird units like “kilopond” which is the weight of a kilogram, and “dyne” which is one ten thousandth of a Newton, or “erg” which is 1/10,000,000 of a Joule (and there were no Watts, or kWh)

It was simply found that bumping the mass standard up a 1,000 fold was more convenient than changing the length standard to a kilometer to get the units to align better with reality.

18. I’m a big fan of decimal inches, it’s more natural than metric without the funkyness of fractions. The precision of .001″ is a good fit for most manufacturing processes. I can use both interchangeably, but I end up using fractional millimeters(2.125 mm or 3.25mm) instead of tenth millimeters(2.1mm or 3.3mm). If I was god-king of the world I’d make a system that has the unit interchange of metric (mm3=ml=gram of water) but units in powers of 2 and fractions of powers of 2 kind of like US liquids work in terms of pints, quarts and gallons. I find base2 divisions much more natural and pleasing design wise.

1. Greenaum says:

Decimal inches, best of both worlds! Erm…

Powers of 2 I suppose are easier to divide, in that you just shift right. If you’re dividing by powers of 2, that is. Otherwise you end up in base-2 long division, which must be pretty hard to keep track of. Maybe hexadecimal as a compromise, if you could go back and change the number of fingers people have.

Problem with binary is numbers get very long very quickly, there’s not as much information density in the digits.

19. ville. vaisanen says:

I am so very happy for living in a country, where only metric system is being teached.

20. notarealemail says:

Hey [Bob Baddeley], great article! I give it a 15 out of 16 inches. :D
The measurement wars have escalated to a wonderful level and there will be converts to ‘The Dark Side’.

21. wernicke says:

The beard-second is one of my favorite units of distance. Google (google calculator) will even do conversions for you.

22. TheRegnirps says:

One beef about Imperial versus Metric. They are both metrics. The French metric became SI and the Imperial metric is just called Imperial. “The metric system” is totally ambiguous. At least I think so the way it is used here. Those saying “metric” I think mean SI and should say SI so we know which metric is being used.

The old units are worth knowing because of the way the make history concrete. A mile (thousand) is 1000 strides – lets say 1000 times the left foot is used – by a Roman soldier. And it works pretty well today if you are wearing a pack and not racing. A furlong is the length of a plow furlough (furlough’s length) along side a road and marks off a King’s Acre, the portion of the land that represents taxes. A yard or cloth-yard is the amount of material it takes to make a set of clothing. One yard by two yards. The inch, foot, yard, pint, quart, etc are single syllable words that will not be confused on a noisy work site and git the human hand and working ability. The whole land measuring with rods and chains and all is fascinating, and it worked really well.

The factor of 10 nature of SI is great for calculation but not very suitable for applications. My scope dials go 1 2 5 10 20 50 100 200 500. In other words, factor of 10 steps are too big. Same for the volumes. “Can I get 500 mm of wodka?” “Sure but it will take a while for me to count it out.”

1. Jii says:

“500mm of wodka”? Millimeters are not a unit of volume, and do you mean vodka?

1. RÖB says:

Wodka is what Vodka is after the first 500 milliliters.

2. bzyzny says:

I believe wodka is correct spelling in Polish, and yes it should be 500ml, or 0,5L is also common.

1. The L when used for liters/litres should be lower case according to SI. Something that most Americans get wrong.

Oh well… I guess it’s not as bad as saying “Calories” when they mean “Kilocalories” (1000x difference).

2. Greenaum says:

Yes they both measure quantities, which I suppose makes them both metrics, but one is Metric!

The fascinating and utterly arbitrary origins of Imperial measures are interesting in an historical context, but they should probably stay there. A yard is probably bugger-all use to a modern tailor, who makes shirts that actually fit, and a King’s Acre isn’t much use in the suburbs. The problem with feet is that people have different length feet. Back when you wore sandals or clogs or whatever that probably wasn’t as important, but I bet they weren’t as comfy as properly measured shoes.

The point of Metric isn’t powers of ten, it’s base ten. As in it’s really easy to add or multiply any amount of metres or cm or kg together. That isn’t the case for feet / yards / furlongs / Christ knows and pounds / ounces / cwt / short tons / the whole horrible dynasty.

We’ve put men on the Moon, it’s about time we had a measuring system that’s actually sensible. We have calculators. We have mass literacy. A bizarre mix of measures that were made up from scratch, and then we all stuck with for millennia, have had their day. We DESERVE a sensible system that’s easy and logical to use. It’s 2016! Or 13, 5 and sixpence in the old analogue calendar.

1. Yellow Four says:

“We DESERVE a sensible system that’s easy and logical to use.”

Then we should be using base 12, not the clunky, inferior base 10. If you want one reason SI isn’t appropriate for everything, this is it. When we start adopting a better practical base, such as 12, then we can all move forward to a truly useful, universal, unified measuring and counting system. SI under base 10 will never gain any more traction in U.S. and many industries that want better fractional and human-relatable units.

2. Yellow Four says:

“We DESERVE a sensible system that’s easy and logical to use.”

Then we should be using base 12, not the clunky, inferior base 10. If you want one reason SI isn’t appropriate for everything, this is it. When we start adopting a better practical base, such as 12, then we can all start using a truly useful, universal, unified measuring and counting system. SI under base 10 will never gain any more traction in U.S. and many industries that want better fractional and human-relatable units.

3. Dax says:

” A mile (thousand) is 1000 strides – lets say 1000 times the left foot is used – by a Roman soldier. And it works pretty well today if you are wearing a pack and not racing.”

Except the average human stride length is closer to a meter, so your thousand pace mile is about a third short.

And vodka is measured in centiliters. 50 cl of vodka is a half a liter, and why would you measure them individually? A centimeter of liquid in a typical cylindrical shotglass is approximately 1 cl. A fingerwidth is about 1½ cl.

If you want to make it more accurate, the glass should have an inner diameter of 3.57cm.

23. RÖB says:

Not mentioned here is some of the issues with smaller screws. Metric is fine M3 is 3mm M4 is 4mm etc but Imperial is mor complex.

For screws of a size that hacker would work with imperial is confusing there is UNF and UNC for Fine and Course thread but some fine thread imperial screws are on the UNC scale because of the time they were introduced.

Also screws smaller than 1/4 of an inch are measured by sheet metal gauge rather than a fraction of an inch.

For example those screws that hold a floppy drive in are 4/20 which stands for 4 gauge thickness and 20 threads per inch. This is something that most people have forgotten.

Imperial units will eventually disappear. You Mericans seem to be propagating them longer than need be. You Mericans keep telling us how many challenges there are to convert to metric but we non-Americans just say “well we solved them decades ago”.

For now we have to deal with it.

Merican imperial volumetric units are also different to other imperial volumetric units. This has cause a couple of air craft to fall out of the sky – sucks when volume of fuel you loaded is far short of what was expected or needed.

I use express PCB for making one of PCB because I change the component footprints to suite a makeshift etch process. Changes like making the holes on through-hole as small as possible so that I can use the small hole as a drill guide.

When I change from metric to imperial grid it seem to snap all the components to the new grid. Anyone know of a fix for this?

1. Greenaum says:

It’s only difficult to convert to metric because you have to convert, and it’s the Imperial measurements that make it difficult. It’s an utter piece of piss to convert volume in centimetres to litres. It’s just as hard to convert one Imperial thing to another, like how many pints in a 6 inch cube.

The solution, of course, is to throw out Imperial. In Britain we still have a few old measurements, like pints (only for beer), and miles on roads. We might say something’s around a foot long or a metre, depending on which length it’s closest to, but if you were going to measure for, say, a new carpet, you’d definitely use metres, because it’s easy to multiply into square metres. Also we measure body weight in stones and pounds, because nobody really has any idea what 150 pounds actually means, is it thin or fat? Same with kilograms. Body weight is something we’re just used to using stones for.

Eventually we’ll abandon that, all medical uses use kilograms and metres. It’s just colloquial. And the last few generations have all been taught Metric at school.

1. RÖB says:

I don’t personally have trouble covering common imperial units to Metric because I grew up and was taught imperial to start with. Our country only changed to Metric in 1972. One of my PCB CAD software application seems to have a lot of trouble with the conversion lol.

I find it completely ironic that America is *stuck* in imperial when the original creators of imperial (The British) have long since abandoned imperial in favor of Metric. lol

I still use some imperial when it’s more practical. For example I am making a PCB CNC and I chose 5/16th inch threaded rod (18 threads per inch) which is very close to the 8mm (ID) bearings at 7.9375mm so it is easier to do the math accurately with an 8 bit micro – given that most PCB dimensions are still imperial.

The bigger problem with imperial is the fractional math is not taught anymore and hasn’t been for quite some time so most people don’t have the mental training to do fractional math easily in their heads and most common calculators are completely alien to fractional math.

1. Greenaum says:

Are you sure about fractions not being taught? I’m pretty sure they are. That’s nothing to do with measurement. We learned that and “decimals”, aka floating point, as well as eg 5×10^7 notation. I had a calculator in the late 1980s, a Casio with “Direct Algebraic Logic”, that could do fractions, it wasn’t expensive, about a tenner. Also did remainders. As an option, of course, it also did standard floating point.

1. RÖB says:

Well I am sure that fractional math hasn’t been taught in my country for a long time but that may be because we went metric in 1972 so fraction math is less commonly used for simple tacks.

If imperial is still in use in your country then I would hope that fractional math is still taught is schools.

The 80’s was about the last time I saw a calculator that could do fractional math. In fact I think it was a Casio FX80 or FX82 from memory. I’m sure they still exist but I haven’t seen one for a long time. My kids can’t mentally do fractions and they’re quite intelligent one is a scientist.

Even my windows calculator which has several modes can’t do fractional rationalization.

2. notarealemail says:

They are taught in the US but very very poorly. The math teacher I had taught some great math trick involving fractions but he was the exception.
Math classes have taken a big hit recently; they allow calculators during simple test that should only require pen and paper! It is sad and I’m worried about the future of my country.

3. Greenaum says:

My country, such as it is, is the UK. But I can’t see why they don’t teach fractions in yours, that’s actually really worrying!

Fractions have nothing to do with Imperial measures, they were just around at the same time. Actually I suppose it’s easier to work with fractions in Imperial, since 1 inch is some horrible long part of a foot (0.08333, 3 recurring), if you write it out as floating point. 1/12 is easier. But that’s not the only use for fractions! Genuinely surprised your country has abandoned them, and a bit horrified. I left school 20-odd years ago, so maybe I’m wrong, I’ve got friends who left 10 years ago, I’ll ask one! Or I’ll look up the UK’s National Curriculum, or whatever they call it now.

Fractions crop up in everyday life more than algebra does, or geometry. And it’s only since I do a bit of programming that I’ve ever had to use algebra, though it is good mental exercise, it’s a mode of thinking that can apply to other things. Proper logic is something they really, really need to teach at school! People are just too irrational, proper logic skills would improve society overnight. That, and the Scientific Method. People need to know how to discern truth over opinion, and most people aren’t equipped to. Even then, they probably won’t. But at least they’d know how!

24. Skateboard trucks have a mm length for the hangar and inches for the axle length. Wheels are in mm.

25. Sure, let’s not mention slugs. Or the difference between pound mass, pound force, and slugs.

Slugs: Unit of mass. Constant conversion factor to kg.
Pound mass: Unit of mass. 32.17 (g) slugs.
Pound force. Unit of force. On Earth, often has the same value as pound mass.

26. foobar says:

Honest question: I’ve got a bog-standard pair of calipers. I can read the metric side easily (tenths of millimeters), but I cannot figure out how to read the tiny fractions of inches. any help?

1. RÖB says:

There are many different types of calipers. Dial, Verier, internal external, depth, thou/mill, hundredths, fractional, balled, lateral, extensible, pivotal.

27. Alan says:

It’s not a meter, it’s a metre. Invented by the French.
A meter is a measuring instrument.
10,000 kilometres is the distance from the equator to the North Pole, using a straight line at 90 degrees to the equator that passes through Paris…

1. bzyzny says:

I always thought metre was the correct spelling (although autocorrect doesn’t agree). I get a lot of weird looks for using metric in USA as it is, spelling it correctly would surely make me an outcast.

1. Daniel says:

According to dict.leo.org it is spelled metre only in good old Britain.

1. Greenaum says:

Many other sites tell me “meter” is just the American (mis-)spelling. Everyone else uses “metre”, which is correct. I put “meter” down to American unfamiliarity with the term. Have a Google. It comes from “metron” meaning “measure” in Greek. Same root as “meter” as in volt meter, I suppose.

2. Greenaum says:

http://www.metricationmatters.com/docs/Spelling_metre_or_meter.pdf

This is a very interesting page for pedants who are into useless knowledge (ie me and most of us here).

“From 1797, the metre spelling became common in all English speaking countries, including the USA. For example, Benjamin Franklin, Thomas Jefferson, and John Quincy Adams all used the spelling metre”

I bet it’s that little twat Webster again! Curse him! The dictionary one, not the one from the sitcom I’ve only vaguely heard of.

28. cbob says:

And a very long time ago my 1973 Ford (pinto wagon – EEK) had a German built Ford motor. Adjusting the valve clearance was…Interesting. It required metric & SAE (inch) wrenches to be used at the same time. Amazing car…It self composted, served as a example of how not to design a car & proved just how many corners could be cut on safety and get away with it. (in the words of Beldar – broken down, rusted out shitbox)

1. RÖB says:

I once had to repair an old printer from around that era. I think it was a Wang! It has a motor that had a US housing and a Japanese rotor and as a result it had bearings with OD 1/2 inch and ID 8mm. Took me a damn long time to find a replacement.

29. Just a point of note about the use of imperial measurements outside the USA. Yes, we use inches for TV screen size and wheel size for traditional reasons but those numbers are only used comparatively. So we may think 55″ TV for the living room or 32″ TV for the bedroom but when we come to actually measure a TV to fit somewhere we are going to get the actual exact specs in metric and cut holes or buy furniture specified metric measurements. I think in time even that traditional use will fade as we have several generations of people who have no way of visualising an inch without thinking of a TV or wheel, it has no other real world meaning to them.

30. TheFinn says:

Strange that when I get machines from Canada (Bourgault, MacDon), they use standard hardware instead of metric. Guess they were too cheap to re-tool their factory lines.
Oh Christ and Buddah — why am I commenting on a religious discussion?

1. You see the great thing about “standards” is there’s so many to choose from! :-p

1. notarealemail says:

Grrrrr…
USB cables…

2. i was trying to hint at the dilemma, most non USA citizens face, reading articles/comments on HaD or elsewhere:
If the author uses “standard …” when referring to “United States customary units” (or sth. similar) many people won’t know exactly what was meant.

31. kessel run says:

Don’t forget electricity, 110v imperial (or “English” if you will) is ~ 240v metric. Can be quite dangerous to mess that up…

32. Galane says:

The absolute worst systems of measurement are in pipe and plumbing. They’re mostly all nominal sizes. Nowhere in all of the pipe and fittings available in the USA is there anything that encompasses 1″ diameter within the thickness of its walls. Every bit of it either has an ID larger than 1″ or an OD smaller than 1″ – yet there are pipes and fittings highly inaccurately called “one inch”.

Polyvinyl Chloride (PVC) pipe uses IPS (Iron Pipe Size) so its pipe sizes are somewhat comparable to galvanized and black (not zinc plated) “iron” pipe, which are both actually made of steel. Genuine iron pipe is very different on sizes, mostly used for drain pipe, but it used to be used for water mains too. *Those* sizes were adapted for ABS plastic pipe. In actual iron pipe 3″ is pretty close to 3″ ID, but as sizes get larger the actual ID progressively gets larger than the nominal size. ABS is even worse at this because its walls are thinner than cast iron pipe of “equivalent” nominal size.

The threaded fittings for PVC and ABS are the same sizes as the metal ones they’re based on.

Then there’s CPVC which does NOT stand for Chlorinated PVC, nor does it denote that it’s made to withstand higher temperatures than the white IPS PVC – even though you’ll likely only ever see the higher temp brown CPVC.

The C in CPVC is for *copper*. CPVC was developed as an alternative to copper pipe and thus is made to be comparable to CTS (Copper Tubing Size) which is entirely unlike IPS (steel) or actual iron pipe. At least CTS sticks to IPS dimensions when it comes to threaded fittings.

There are commonly available adapters to conjoin *most* sizes in and between the three systems, in metals, plastics and even insulated ones to prevent galvanic corrosion when linking up different metals.

Yet in NONE of those three very different pipe sizing systems is there any pipe or fitting that can be put on a lathe and bored out or turned down to precisely 1″ diameter. I know this because some years ago I did a project that required a ring to be turned to 1″ outside diameter and I dug through all the stuff at hardware stores and plumber’s shops, coming up empty. I even tried Type K 1″ copper which is supposed to have a 0.995″ ID. Well it didn’t and even if it did that would only have left 0.005″ thickness. If one needed a copper tube (say for a model steam engine cylinder) for a precise 1″ bore, you’d have to sort through a lot of Type K 1″ tube to find a piece with consistent enough ID to be able to get a smooth finish with a 0.005″ cut.
I finally found that a brass nut for some propane gas fitting would work by boring out the threads then cutting off a large amount from the hexagonal outside would work. As least *one* field of moving stuff through a tube didn’t find the inch so abhorrent. I only made one of the item because drilling, boring and turning the parts from solid chunks of copper or brass would have been far too time and money consuming. So would buying those propane fitting nuts.

That’s one thing I’d do with a time machine. Go back and give accurate rulers to all the people responsible for the mess that is plumbing dimensions. “See this? THAT is an INCH! Not 1-1/8 OD with a 1.055 ID!” “Why is this 48″ iron pipe over 49″ inside? What are you measuring with? A stretched out cloth tape? Or is it a piece of wood carved with notches estimated by eye and the first joint of your thumb?” Get that crap sorted before metal plumbing became a big deal.

1. RÖB says:

My country saw these issues coming and mostly avoided them. With gas which is more of a safety issue we just switched to left hand threads so that gas fitting are specifically for gas and nothing else.

1. notarealemail says:

That’s a brilliant idea they had there! :)

2. Greenaum says:

1. RÖB says:

Australia: where lethal creatures are a protected species and non-lethal creatures are extinct.

1. Greenaum says:

Ah, where the beer does flow and men chunder!

2. enl says:

A couple points:

The history of pipe and tube sizes is bizarre to modern eyes, but actually has a logic. The logic is that threaded pipe of the same nominal size has the same outside diameter. The sizes were specified several rounds of technology ago (wrought iron pipe with forge welded seams, according to several sources on my bookshelf), and as materials and uses changed,, the OD was held, but the wall thickness changed to meet requirements. For your 1, try 1″ nominal schedule 80, with an ID of 0.96″. I have bored plenty of this out to 1.000″ For slightly smaller ID, use SCH160. Home depot doesn’t have it, but any reputable plumbing supply (or local hardware) shop will.

For the copper, it is a bit simpler, but due to the cost of copper and the applications, you don’t have the excess wall thickness as in steel. But you can generally design around that, if you need copper. Design for the available material. Generally, pure copper isn’t used for precise dimension items like a shaft bushing, as it is a bit soft and sticky. Brass and bronze have more variety than steel, so it isn’t much of an issue.

CPVC does mean Chlorinated PVC. It has a higher chlorine content (you can google for the process) such that it is suitable for higher temperature than standard PVC. Yes, the intent is, in part, replacing copper in domestic water service, but the reasoning is temperature. Since there is no practical way to join CPVC with copper other than a threaded transition or special compression fitting (standard copper compression fittings don’t play well with PVC/CPVC. The pipe cracks), there isn’t a reason to match copper dimensions, and there is advantage to matching iron pipe dimentions (the abundance of threaded fittings). Both PVC and CPVC, as well as PEX, are available in sizes to match copper plumbing, though it can be very hard to find. In most of the US, PVC and CPVC are seen mostly in iron pipe sizes and specialty fittings like sink drain fittings like tailpieces and traps (which match little else).

33. I’m frustrated with US units on home improvement projects. Fractional inches on measuring tapes and decimal inches on calipers. I made an insert to fit a sliding glass door frame; extruded aluminum with various channels and ridges. I needed the measuring tape for distances over one inch and the calipers for details under one inch, and then I had to add things together. Annoying to mix them all. I changed over to metric, and everything was in whole millimeters. Great!

It’s not hard to find measuring tapes with both inches and meters. The problem is that sometimes you want to measure from the left and sometimes from the right, so it really helps to have a metric-only measuring tape, and a metric-only framing square. (I found framing squares with inches on the outside edge and mm on the inside edge. What?!) Can’t find them in any US store, or almost any US mailorder company. Not on amazon.ca or ebay.ca either. Had to go to ebay.co.uk and ebay.com.au to find them. Ordered a few 3m, 5m and 8m tapes, and they are great. Finally found a 400x600mm framing square on ebay and guess what? Made in USA, just not sold in USA. Argh!

Laid out a laminate wood floor in mm using the 5m and 8m measuring tapes. Measure across room, divide by 2, split the difference. Piece of cake in whole mm. Never doing that with fractional inches again! And, especially easy since the nominal 5″ boards were actually exactly 125mm. Even without that, working in whole mm is great.

1. notarealemail says:

I like fractions of an inch.
I can turn them into decimals and back to fractions inside of my head.

It is like magic or something. :P

34. John says:

I got endless stick in Greece for using inches pounds, stones etc etc. One day the guy I was working with was blowing his car tyres up so I asked him what pressure he put in. 30 was the reply, 30 what says I, I don’t know says he.

The use lb/in^2 but don’t know it.

35. Good of us, ” you all ” to talk about this, it reduces the pain, and links us tighter to make a better live-able World. With my glasses 1/64 was always a strain, so i got a magnifying glass, and tackled the 1/100 dred conundrum. i, us, really need to get to some good fraction of 1/1000 thousand, th, of what were working. for me 2 parts in 10,000 parts, for my pc printed circuit work, so, i bought one of those slip in ccd scope thingies, and it works great. i am a happy camper now. good to read the comments, here, feel at home, Cheers, all,

36. Jim says:

I’m surprised no one has mentioned smoots. Hey it’s a unit of length in Google Earth.

37. The U.S. does not use the ‘imperial system’. The correct name for the U.S. system of measurement is the U.S. Customary system. It was based on the british imperial system, but is not the same thing.

38. Marc T says:

Am olde-world British. I had, for a short time (6 years or so) experience with LSD (not the drug) but had little or no trouble with decimalisation – I suspect this was due to the fact that 6-year-old children only appreciate what the money can buy not the actual value of it.

For many years whilst still in the UK I was happy dealing with a mixture of both: money in base10 and weights in Imperial. The years have seen me end up in various parts of the world (none of them West of UK) and the gradual erosion of much of the older systems. However, I still use a mixture of old and new: old in the UK and new everywhere else. Old being distance and velocity, eg., Rugby to London by rail = 62 miles, 1 hour approx at 60 miles per hour – but will always use metric for construction/engineering purposes – as in metres and millimeters.

I worked in construction for a few years and we measured everything with our body: a closed fist = 4in; spread fingers (tip of thumb to tip of little finger) = 9in; from tip of thumb to first joint = 1 1/2in; tip of index finger to second joint = 2in; fist knuckles to elbow = 18in; arm span (in my case) 6ft; size of foot with shoe on = 1ft (UK size 11 1/2). All these are approximate but that was easily sufficient to put up scaffolding to the point it bceomes practical for use and far faster than constantly whacking out a tape and measuring up.

The Racing wallahs who buy and sell horses and some sheep trading in UK still operate in guineas: 1 guinea = 21 olde shillings = 1.05GBP.

39. Marc T says:

…oh! and don’t forget paper sizes. The world using a standard format A0-A(whatever) and the ‘merkins still using ‘letter’. I have no care what the actual dimensions are but the fact that the bulk of the business world uses A-standard but we have to keep adjusting for digital documents sent from the US-of-A.

..and finally, the weather. In Blighty we did away with temperature in Fahrenheit over a period: weather presenters delivering in degF and degC for a while, now all temperatures are delivered in Celsius/centigrade but you guys in ‘merka still operate in F and I have no idea how hot that is in new money.

1. I’ve been to a swimming pool in Canada which had a board showing air temperature in Centigrade, and water temperature in Fahrenheit… Or it might have been the other way around, but in any case it was confusing as heck :-D

2. Dax says:

There’s actually more standards than just the A standard – there’s A, B, C which are slightly different sizes, but the order from smallest to largest is actuallly A, C, B. The A series is used for documents, the C series is used for envelopes, and the B series is used for print and books.

Then there’s also national extensions to the standard that may add sizes D,E,F,G between the major ISO standard series.

40. When I was growing up in the Netherlands, pretty much everything was metric except for some things in foreign (especially English/British) cars.

Then came the IBM PC which was mostly imperial, but when hardware makers switched from full-height to half-height 5.25″ drives, they introduced metric and mixed it all up.

I’ve lived in the USA for almost 16 years and it took me probably 4 years to find out how many yards are in a mile (though I figured out quickly it wasn’t a nice round number, nobody seemed to know the exact number), and that a “Pint is a Pound, the world around”: 128 fluid ounces in a gallon, a quart is (obviously) a quarter gallon, a pint is (not so obviously) half a quart and a cup is half a pint (where I come from, a cup is just something big enough to drink tea or coffee from, it doesn’t have a predetermined size).

Oh well, I got used to the empirical distance, volume and weight measurements and I’m at peace knowing that an inch is 2.54 cm by definition (not by approximation) so even though Americans are the worlds only knuckleheads that just don’t want to get with the decimal program, I know they’re really using the metric system all along, they just have weird names for weird amounts.

And Fahrenheit to Celsius is also pretty simple in daily life if you can remember the numbers 32, 50, 68, 86 and 104.

===Jac

41. esde says:

1 inch = 25,4 001 mm. this ..001 is often missing but sometimes VERY important. Mostly when you try transform production from one to another system.

1. RÖB says:

One inch is internationally recognized to be exactly 25.4mm. Mericans decided it would be better that there be exactly 39.37 inches to a meter so they modified the inch to be 25.4000508001016mm.

Only Mericans do this. It is NOT acceptable anywhere else in the world. The Mericans can have their *confusion* while the rest of the world sticks to official SI units.