1 mil is equal to one thousandth of an inch 0.001″.
I was a bit confused the first time I learned about mils, but it’s something I only had to learn once.
Mils are less cumbersome than decimal points and a bunch of zeros.
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What’s easier to read or say? 0.0043″ and 0.0071″, or 4.3 mils and 7.1 mils?
Mils are used in other engineering and manufacturing contexts, and sometimes thousandths are used instead, at least colloquially. I see mils on paper more than thousandths, but hear thousandths verbally more than mils.
I usually encounter specs in mil units when shopping for plastic products.
For example, the food-grade buckets I use are advertised as having a 90 mil wall thickness. One style of disposable nitrile gloves I use has a 4.3 mil palm thickness, and 7.1 mil finger thickness. The plastic pouches I bought for food storage have a 3 mil wall thickness.
Try not to confuse mils with millimeters. That’s probably why thousandths/thou are spoken about more in lieu of mils.
1 mil is equal to 0.0254mm, which is 25.4 microns. That’s pretty far off from 1mm. 1mm is equivalent to 39.37 mils.
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If you like the idea of mils, you’d probably love the metric system. Similar to how 1 mil is 0.001 inch, 1 mm is 0.001 meter, and 1 micron (µm) is 0.001 mm.
No – this isn’t an invite for anyone to start an inch/imperial vs metric fight. But if anyone is interested, let me know – that could be tomorrow’s post.
Birdog357
I’m a drafter and I’ve worked with a lot of machinists over the years. Never once has mil been used in any conversation. I actually didn’t even know it was equal to a thou…
MM
I think it’s one of those units which is popular in some industries and not others. I heard the term very often when I managed a University materials lab. We did a lot of work with polymers and it is extremely common in that industry for the thickness of films, bags, etc. When I had my machining business afterward I can’t recall a single customer specifying anything in mils though I came across it buying plastic bags or sheet. In fact in my experience around machine shops in general was that “mil” was never used because it could be easily misunderstood to mean “millimeters”. We’d say “thou” for thousandths of an inch instead of “mil”; a “tenth” meant one ten-thousandth of an inch.
Rafe
In the coatings industry it is used a lot, but Ive never known anyone who uses the measurement in a relevant way. Im sure a tech who operates an automated system would measure mils in their application process but virtually no one else.
fred
Wet-film thickness gauges often measure in mils:
https://www.amazon.com/Nordson-Type-Film-Thickness-Gauge/dp/B088MNJSVJ
Ben
If you go buy some plastic sheeting at Home Depot it’s sold in mils. About the only place that I can think of mils being used in semi-normal day to day use.
fred
They also show plastic bag thicknesses as “mils”
Adam
It’s also used to describe the thickness of the wear layer for luxury vinyl plank (LVP) flooring, i.e. 20 mils represents the boundary between high end residential performance and low end commercial
BigTimeTommy
“No – this isn’t an invite for anyone to start an inch/imperial vs metric fight.”
That’s fine, there’s nothing to fight about, because metric is inarguably better 😎
TomD
Especially poetically! I love all the songs about how “she has a smile a 1.6 kilometers wide” and “you load sixteen metric tons and what do you get”.
The best of course is (as is all too common) when an industry just randomly mixes all forms of measurement with no regard for anything like standardization. 2cm wide and ten feet long. 9mm barrel in the 8 inch form factor. Kilogram-miles.
IronWood
I always loved Tony Rice’s “4.08 kilogram Hammer”
William Adams
The bottom line is, since the Imperial inch was redefined in terms of a millimeter, customary measure is, underneath it all, metric.
That said, it’s a matter of interface, and sometimes using small, neatly divided decimal measurements makes sense, so metric, or one wants a description which folks are familiar w/ or which rhymes.
Other times, one wants a conveniently larger unit to keep the numbers reasonable, so inches or feet are more workable, or one wants the ability to do divisions which don’t fit neatly into base ten (10), so the ability to divide a foot into 12 even divisions (or 3) can be quite handy — I will frequently get a rule from my graphic design days which divides an inch into 72 PostScript (big points) and modern Picas (6 per inch) (as opposed to the older measures such as 72.27 printer’s points per inch) which makes for nice easy math in many instances.
(One of my constant complaints of templates done by folks in metric countries was multi-column layouts where the spec. width of a 2 column wide ad did not equal (column width * 2) plus gutter width in a three or more column layout.)
It’s rather a shame that the Japanese when they created a metric measure for type units, the Kyu (one Q(uarter) of a millimeter) they didn’t pick 1/3rd — having that to fall back on for such would have been a nice compromise.
One interesting thing is that many imagesetters use a pixel grid of 1/1270 or 1/2540 inches, which neatly fits either metric or Imperial measure.
MM
My favorite ruler, which I have no idea how I came to possess, is marked “Moore Business Forms” and has some interesting scales on it. In addition to the usual inch scale graduated down to 32nds it also has an inch scale with markings at 1/6 and 1/12, another in 1/10, and the fourth one is in units of 5/32. The 32nds inch ruler also has markings for “Cards”, which as best as I can tell is 1/140th of an inch.
fred
Probably to measure a stack of Hollerith cards. There were once thousands of keypunch and verifier operators putting little square holes into (and checking them) producing stacks of these cards to both program and input data into mainframe computers.
Jim Felt
@fred. Exactly. I wonder if Moore itself which was certainly national still exists?
fred
From what I can read online – it looks like Moore merged with Wallace Business Forms to become Moore-Wallace – which was then merged with RR Donnelly (RRD) that now operates Moore Business Forms as a subsidiary.
MM
Speaking of older data systems like punchcards, I find it interesting that even today high end screw machines and Swiss-style sliding headstock lathes have their program (memory) capacity rated in “meters of tape”, a hold-over of the days when punched paper tape was used to control machine tools.
Michael F
Well, since you started it, I wouldn’t say inarguably better. In fact I’d argue Imperial is better for many things, especially architecture. Why? Because you can divide imperial units evenly by more than 10, 2, and 5. You can divide Imperial units (feet specifically) by 2, 3, 4, and 6! The system of measurement you use tends to influence the entire philosophy and it’s well known that the golden ratio (roughly 2/3rds) is the most aesthetically pleasing to the human eye. Putting two windows in a wall, both a third apart, is easier (at least philosophically) when using the Imperial system. Some would argue this is why countries that adopted the metric system sooner tended towards more brutalist architecture. Anyway, considering 3.33 meters is a perfectly valid measurement I must admit the argument is pure philosophical.
Stuart
It depends. Are we talking about integer measurements?
24 inches is evenly divisible by 2, 3, 4, 6, 8, and 12.
60 cm is evenly divisible by 2, 3, 4, 5, 6, 10, 12, and 15. 60/8 is 7.5, which is well marked on metric tapes.
What about dividing by 9? 24/9 is 2.67″, which is where on a tape measure? 60/9 is 6.67cm, which is right between 6.6 and 6.7cm.
2.67″ is less than 2-3/4″. So, between… 11/16″ and 3/4″? No. Umm… between 5/8″ and 11/16″.
There are pros and cons to both. Inches and feet aren’t all that bad when working with decimals. How do you measure to say 4.2 inches? You need an engineering rule. 14.2 inches? You need an engineering tape, which you almost certainly won’t find at the home center.
fred
But it sounds like I weigh less in Britain (15 stone) instead of 210 pounds. 15 seems lighter than what my weight would be on the moon in pounds (about 35) or in France in kg (about 95).
At least the Brits have gone over to the decimal system for money. The first time I was in England (1959) there were still farthings (1/960 pound) , ha’ pennies (1/480 pound), pence (1/240 pound), “tuppence” (1/120 pound), truppence (1/80 pound) , shillings (1/20 pound or 12 pence), half crowns (1/8 pound). At least they had gotten rid of guineas – but some merchants still quoted prices in that denomination (1 pound plus 1 shilling)
Andrew
Still there for horse racing
tim Rowledge
The guinea was essentially a 5% tax on the wealthy. Charge’em guineas instead of pounds and get revenge on the grasping toffs. Used largely for horses, ladies of high-priced negotiable affection and ugly paintings
MM
Guineas remained in use for things like professional fees, i.e. hours billed by an architect, lawyer, or doctor, and for fine bespoke work like a Seville Row suit, John Lobb shoes, or a Purdey shotgun long after decimation.
Cory
Menards used to have the Stanley 25′ LevelLock Engineer’s Scale tape measure in their stores. I purchased one there. It’s easier to do fill calcs (concrete) when you don’t have to do inch conversions.
Home depot sells it… it might be available locally:
https://www.homedepot.com/p/Stanley-LeverLock-25-ft-x-1-in-CC-Center-Tape-Measure-STHT30758L/204624317
Birdog357
4.2 is 4-3/16(4.1875 rounds to 4.2) that’s not hard to figure out. 4.20 is still 4-3/16 because 4.19 is only 10 thou off and I really doubt your tolerance is that tight if you’re using a rule to measure… 4.200 requires calipers/micrometers to measure anyway…
Stuart
Yes, you can sometimes approximate and round to the closest fraction. It depends on what you’re working with and whether the differences will stack.
SAMO
Metric temp is way too corse. F is a much better finer system.
Stuart
I agree, although if we had to I’m sure we could get used to half-integer temperature settings.
68°F is 20°C
72°F is 22.2°C
So instead of setting the thermostat from 68 to 70, one would go from 20 to 21. If an in-between setting is needed, there’s 20.5.
Bob L.
This conversation has been repeated many times and a mil has a different meaning to many people. Do not just throw the term out in a conversation. Say what you mean in clear English.
Wayne R.
I believe that everyone should try to avoid terms that are easily confused. But each generation’s colloquialisms always seem to go out of their way to be obscure at the same time as being ubiquitous. Humans: We’re our own enemy.
James Vis
As an engineer who works in the imperial (US) system but also has to work with many international companies, I regularly have to switch between imperial and SI (metric). I grew up learning metric (in Canada) but moved to the US post highschool where I live and work and learned imperial system.
I can honestly say that simply learning the metric system is much easier as it uses a base 10 system. BUT, making a change from imperial to SI in the USA would take a literal act of Congress as well as political determination for several decades.
It would realistically take a full generation or more to completely change to metric and the cost to do so would be astronomical. Think of all the road signs, food labels (in food safe containers😁), textbooks, manuals and specifications, etc. The time of a generation is necessary because you realistically need a brand new generation to grow up in the metric system and become the primary work force.
I like both systems, but prefer imperial because that is what I have known my whole career. I am glad that making a decision like this is not something I would be in charge of.
Happy debating and happy Friday!
Schill
Congress passed a law in 1975 essentially saying the US should switch to metric. That made the metric system a very important part of my elementary education. Teachers actually emphasized it.
I “grew up” to be an engineer in an industry that has a lot of historical data in both systems.
I’ve been comfortable jumping back and forth between systems since elementary school.
I think all the US got out of the 1975 law was 2 liter soda bottles.
Rob G Mann
Yes, I remember Highway signs being in both formats as a child.
We got 750 ml liquor bottles in addition to the 2 liter soda bottles. 😂
Wayne R.
When I was a kid, the whole idea behind teaching “metric” was to focus on conversions rather than just simply using it.
I still stare at the subdivisions on a ruler and have to start counting.
I use metric every chance I get.
Adam
I’m just glad that CAD programs are happy to take either. when I’m drafting up something to 3D print in Fusion360, I tend to work in millimeters, mostly, but if I need a half-inch slot or a six-inch long part (or alignments to one-inch pegboard holes!) I just use imperial for those measurements. As a born-and-bred ‘murican, I did have to print out a little keychain of metric thickness samples to viscerally understand those thicknesses (I can’t picture a 4mm wall vs. a 6mm for example) like I can a 3/16 or a 5/8 inch. But now that I’ve gotten used to it, it is very handy to work in millimeters for small measurements (and nice even multipliers to 3D printer layer heights and thicknesses, which is useful for print quality).
Bonnie
At the end of the day both systems are equally arbitrary, and you can use 10s/100s equally well in both.
OldDominionDIYer
I work in a very large Engineering department and very very rarely hear anyone using the “mil” term, it’s all in thousandths, in writing and spoken terms. While I am familiar with the term it just isn’t used very often.
IronWood
In the shipyard the paint inspectors talk about mils for coating thickness. But the machinists use thousandths for tolerances. It always made me curious how terms get adopted differently among crafts on the same floor.
James+C
How did we end up in a world where mil is the same as thou? If they’re both imperial can’t we at least fix that? What’s the history there? I suspect that’s an interesting story (or perhaps a really frustrating story because this seems like a needlessly confusing situation).
Schill
I worked with a precision machining company several decades ago. Everything they did was measured in “tenths” – a tenth of a mil or 0.0001 inches.
Doresoom
I’m an engineer in the US. It’s common to have conversations discussing “thousandths.” Never heard a single colleague use “mils.”
I’ve also had viewers on YouTube get confused when I use engineer-speak and say something like “ten thousandths” to mean .01″. They thought I meant one ten thousandth or .0001″. So I can see why mils is used outside of engineering environments.
Stuart
Ten thousandths gets me too sometimes too. I’ve seen it mean 0.01″ as much as 0.0001″.
I never see mils mentioned in the context of machinery, such as mils of cuts. I couldn’t think of where I’ve seen it beyond plastics manufacturing.
Ten thousandths is kind of like biweekly, bimonthly, and so forth. It’s not ambiguous, but can equally mean very different units to different people or depending on the context.
Schill
In another reply, I mention measuring in tenths (0.0001 inch). This was in machining carbide bits for cutting tools. The accuracy of the bit geometry (and the multiaxis machines making them) was measured in tenths.
Wayne R.
Reminds me of 10 foot square versus 10 square feet.
Birdog357
Those have very clear and different meanings.
Doresoom
Context is what matters – and having both people conversing familiar with that context. If I’m talking general tolerances, it’s almost always going to be in terms of thousandths (.001). Press fit tolerances in steel? Now you’re in tenths (.0001). Any other engineer I work with knows that, and it’s what makes the conversation easily understood. Someone without that background may not be able to decipher what was meant as easily. But any somewhat proficient woodworker should never have to even think in terms of tenths (.0001), which is what surprised me about being misunderstood.
Franco
I see it on disposable gloves boxes.
Living in Canada, we went metric…not sure late 70’s or 80’s? Anyway, everything is metric but all of my measuring tapes, rulers and other measuring instruments, I always go imperial.
I am an old fart that no matter how much people tell me that metric is so easy, I am too used to imperial and my fractions…nobody touch my 3/8 of an inch (.375 inch…blasphemy!)
ACY
At my work, semiconductor manufacturing, I work on equipment made in the US, UK, and Japan…. We run into the mil vs mm issue with my equipment and alignment procedures. Modern vernier calipers have thousands and mm so training that it is mils vs mms isn’t too difficult.
Other things are more difficult. We need to carry metric and SAE tools due to have some machines using one vs other. The Japanese machines are all metric but the US and UK machines have a mixture.
Air pressure is a strange thing also. We have several units of measure amongst the gauges and software readbacks. psi, psia, torr, micron, pascals(k or M), and inches or mm of Hg.
The pressure unit of measure, micron, is a strange one. It is in torr and equals 1/1000 of a torr. I believe the name came about because it is in the 1/1000000 part of an atmosphere which is 760000 microns at sea level. Aside from my machines, I have only ever seen microns used for pressure in the HVAC industry when pumping down lines before refrigerant fill.
A couple of other strange things I have seen in my industry….
Wafers, the predominately silicon substrate we make chips and other semiconductor devices on, are millimeters in diameter and mils thick.
When dealing with deposition, etching, or penetration of processes we utilize angstroms which is metric but is 1/10 of a nanometer or 10e-10 meters.
Anyhow.. just wanted to mention how goofy the unit of measure situation is in my industry. I could probably think of of more but I have just become use to dealing with all the inconsistencies.
John
Some people act as if it’s never used, but it’s on every packaging for rolled plastic across the country in every home center. Nitrile gloves, rolled plastic, vinyl, paint coatings and the list can go on and on for daily items used in business and homes.
Chris I
Awesome info. As a born and bred American, I’m making the switch starting today and giving/doing all measurements in microns.
Stuart
Switch to Angstroms for a day!
fred
Try ordering a load of concrete in cubic Ångstroms. Of course the common apprentice mistake is to measure the pour in feet and forget to divide by 27. The ready-mix guys will probably catch the error before dispatching 27 trucks instead of 1.
Jim Felt
fred. You’re such an optimist! ;-)~
Charles
I’ve never heard that term in any machine shop. I would have been confused if I saw that on a drawing. Hate doing anything machinist wise in metric.
Kevin
I’ve only ever heard it used to refer to film thicknesses. Everybody usually talks in “thou” or “tenths” (of a thou).
Al
I understand the desire for standardized, inhuman measurement units.
But I’ve never been hit in the head with a 70×35. Is that like a tubafour?
I’ve also shown people how to look for the next stud by spreading you hand, then moving thumb to pinky and scooting your hand over. That’s roughly 400mm, right?
But I also confused people when they asked how many ponies my little 1.5L100hp Honda engine had: 150. More ponies than horses, because Watt made up some measurement by analogue.
Hybrid knowledge is not really a problem, is it? I understand relative engine size by displacement in liters. Power output for a street engine in horsepower. But power output for a generator in W or kW or MW.
My 18.3L diesel genny puts out 650kW, but gets filled up with gallons of diesel. It has a run rate in gph (gallons per hour). Sizing of fuel tanks is “two days” or “48-hour”, with the numerical dimensions being less relevant while roughing out project parameters.
Depending on application, a much larger engine might make 30MW in marine or aviation use. The fuel gets measured in pounds, because that is most important for balance and safety.
All those measurements go out the door when someone asks for speed. That’s in knots per hour. A very, very analog method of casting a rope overboard and watching a sandglass.
I think the crazy measurement article should be re-started once per leap year. You know, because crazy measurements…
Charles
You can really mess with people when you use your fingers and feet to measure things. I’m with you, I grew up with Japanese motorcycles so cc’s and liters are no big deal but I’m not gapping a plug with nothing but thousandths.
Stuart
Looking online, UK suppliers have timber in 38 x 63 and 38 x 89 dimensions.
2×4’s measure 1.5 x 3.5 inches.
British pints are 20 oz, and beverages in the US are commonly bottled in 500 ml, 1L, and 2L sizes ( as well as ounces).
Water freezes at 32°F, 0°C, and 273°K.
Shoe sizes…
Measurement units cab get absolutely bonkers.
tim Rowledge
“British pints are 20 oz,” – and to make life even more fun, British fluid ounces are not the same volume as US fluid ounces!
29.5mL vs 28.41mL Total madness.
Greg
The most aggravating thing about mils is when somebody hears “mil” but then repeats it as “millimeter.” Usually it can be corrected by context, but it would be nicer if that didn’t have to happen at all.
I’ve been an engineer in industry long enough to know to use “thou” with millwrights, “mil” with painters, and “very tight tolerance, which is important but more expensive” with finance/accountants.
James Vis
I love it, and totally understand the finance remark!
Charles
My brother works at the sthil plant in VA Beach and everything is metric there. He likes it but my brain is programmed for imperial, I can’t picture sizes in metric so I’m always trying to convert.
Nathan
Someone beat me to it but I only every see mils with either film thickness of coatings or in terms of plastics – until you get to engineering plastics.
IE things with validated and approved strengths and then I have seem them flip to metric or in some cases use “gage” like sheet metals. But you see less gage being used other than in building now.
Play with airplanes. LOL metric. OK OK get this there is a big multimational company that builds planes in EU. Yeah really and well they must be designed in metric right – well they are I guess. in the drawings frame spacing, stringer dims, etc etc. all metric. the sheet metal specs all metric yet the hydraulic line fittings and the fuel fittings will all snap fit a SAE size wrench. yeah. 7/16 or a 3/4 etc etc. Rivet calls will still be in the MS standards of -6, -8-10 etc. Crazy right.
My favorite though is when you deal with EU operators and they have to specify weights in Kg even when they fly a US build Boeing plane and they use Inch spacing for their weight and balance. so you get units in KG-In when you get into weight moments for balance calcs etc. Or fuel measuring that is KG/in of measuring stick.
anyway. uhm yeah all temp should be in Kelvin, all length should be metric, weight too.
Rob G Mann
I’m gonna try temp in Kelvin from now on. 😝
I lived overseas for many years and my brain successfully adapted to grams, meters, and liters with no problem whatsoever. They are intuitive for me now.
But, for whatever reason, my brain rejected Celsius and I never got beyond other than “-5 is skiing weather, 25 is Biergarten weather, 30 is beach weather”
Min
I’m an engineer in manufacturing and we definitely use mils in common discussion about very small dimensions. I was confused when I first started and I see new people get mils and millimeters mixed up but they learn quickly. I see a lot of comments about how mil is only used with sheet or coating thicknesses but we use it when discussing clearance distances and general dimensions. You won’t typically see it on drawings. We would use inches, millimeters, uin, um, etc. Tolerances in tenths or ten thousandths.
A few tenths, a few thou, 10-20 mil. Just depends on the situation, how large the number is, which one you use and who you are talking to. Many of us probably work in sites where the machine shop talks in inches because that’s what they are used to and that’s what the hard dials say (regardless of DRO), therefore the tools are designed in inches, but the products are in millimeters. Just depends. But anyone who doesn’t know what a mil is hasn’t been around enough manufacturing. Every piece of manufacturing or industry has its quirks and it is tough to get them to “standardize”.
Skyy
I think of Mils from my military days. Pulled from Google;
Mils:
Another unit of measure, the radian, is used mainly by militaries in artillery, tank, and mortar gunnery.
There are 2 PI radians in a circle. PI is a constant of approximately 3.1416. That is 2 * 3.1416, or 6.283 radians. Divide each radian into 1000 mil-radians and you see there are 6283 mil-radians in a circle. Mil-radians are called mils for short.
17.78 mils equal 1 degree.
Compass use of mils typically rounds 6283 to 6400 for simplification. Some foreign militaries have simplified the other direction and divided the compass face into 6000 units, exactly like the face of a watch, with 100 units the same angle as a minute on the watch face.
Using mils, the actual size of an object observed in the field can be estimated. An object that appears to be n mils wide when it is 1000 units away from you, is actually n units wide – the units used does not matter, feet, yards, meters, miles
A vehicle that appears to be 15 mils long and is 1000 feet distant is actually 15 feet long. Or, two vehicles that appear to be 100 mils apart and are 1000 meters away, are actually 100 meters apart.
Conversely, if you know the size of an object, you can estimate its distance from you. If the tops of two mountains are 1 mile apart on your map, but they appear to be 100 mils apart, you must be 10 miles away.
Sighting on a man (approximately 6 feet tall) who appears to be 12 mils tall must be about 500 feet away. If he seemed 3 mils tall, he’d be 2000 feet away.
Stuart
I don’t know about military applications, by radians are extensively used in math and science.
Nate
Good one. Mils always stick with me from that increasing past, 22 year long, life in the Army. And it’s an actual SI measurement!
Jim Felt
Stuart. I see these units misused or ignored occasionally in several activities I’m involved with. I’m glad you’ve helped clarify many of these issues. I’m sending a link to this post to several friends, clients and colleagues.
Kyle Chrystal
I agree that mils are convenient, and for sure they are a common enough colloquial term which is used when working with machine parts and mechanical engineering in the US. I often think of talking in inches when talking dimensions and talking in mils when talking tolerances – of course that doesn’t always hold.
Similarly, when working in metric, it’s really nice to use the micron and there is a similar relationship. mm values when talking dimensions, microns when talking tolerances, surface finish, etc.
Those of us who need to go back and forth between inch and metric frequently get fairly comfortable with common rough approximations… 1 mil ~ 25 microns, 100 microns ~ 4 mils, etc.
Mark Will
I have been working in the building industry since the mid 70’s and love working with the metric system.
Having said that we/I usually say shift/knock whichever the case may be “a poofteenth”.
So we knock/lift/shift it a poofteenth for a minimal unknown amount.
IronWood
I like poofteenth, I might have to borrow that one. At my work we say a “scooch”, with obvious further divisions into half- and quarter-scooches.
Andrew
Mils are pretty common in the PCB industry
Albert
I use thou, and occasionally tenth, but never bothered to find out what mil meant. Now I know what 5 mil nitrile gloves are!
JoeM
I almost exclusively use Metric, and I have never even heard fellow Metric users call a Millimeter a “Mil” before. I’m not sure this is too much of an issue. I’ve only ever heard the term “Mil” used to define the thickness of a membrane or polymer substance that makes up a container. I’ve used a lot of Machinists, especially anyone who was trained by anyone older than the 1970’s as a Millwright or Machinist of any sort, use the word “Thou” to represent “Thousandth of an Inch” but… a “Mil” and a “Thou” are the same size, from all I’ve ever seen their use.
I think, perhaps, this is a use-case-scenario dependent unit. Weight, when measured for a person in the Western world (yes, the US and Canada both do this.) are often weighed in Pounds. Yet, if being measured in Space, or by the Science and Engineering fields, will define their Mass in Kilograms. I think, and I’m genuinely not an expert here, as I’m a very adament Metric user for all my building projects, Mil and Thou are being used in the same sense of units being used to measure how much something is to be removed (Thou) for a machining job to be completed, versus the thickness of something once it has been completed the manufacturing process (Mil)… And I can only use Machinists versus Membranes as the difference there.
But I have genuinely never heard Any use of “Mil” in the Metric system. “Mili” yes, but not “Mil”… Because I think that Metric users figured out there would be too much confusion if we duplicated the terms that way. And I believe our counterparts using Machining in Imperial/SAE would refuse to let us use it anyways, so… it wouldn’t make sense at all to mistake the two.
Andrew
It’s quite common to refer to millimeters as mi. Generally the context makes it clear enough in most cases
Andrew
Mil 🙂
Shawn Y
Isn’t mils just latin for thousand? As w all imperial units, each industry in its inception just created a term to scale w their products’ essential unit of measure for quick and easy com from one industry bro to another at the factory.
I recalled this guy’s video regarding perceived frustrations imperial: https://youtu.be/iJymKowx8cY. Good point in that none of imperial units were conceived as part of a unified system of measure.
My favorite mix of units are tires. I’m running 255mm wide / 40% aspect ratio of sidewall to aforementioned width / 17in wheels.
JoeM
Mili is the Latin Prefix for Thousand-Under Standard. Mili is 1000th of any metric standard. Its equivalent is Millions-Of, which in Latin is Mega, or the Prefix for Thousands Over Thousands.
“That doesn’t make sense” actually, we’re missing something that does. Centi and Kilo share the same relationship. Centi is “Up To One Thousand Under” and Kilo is “Up To One Thousand Over.”
Then it’s just units of measure. Litre (L), Meter(M), Gram(G), Tonne (T) (The only one that isn’t an even 10, as it is 2-thousand Kilograms.)
… I am aware you likely know this already, and I’m sorry if it sounds like I’m being insulting of your intelligence. No, you raised a really good point, and I just wanted to verify for others who may read this. Because it’s worth knowing, and I’m very happy you brought it up.
Stuart
I don’t follow.
Centi is 1/100. Kilo is 1000.
According to Wikipedia, tonne is 1000 kg, and that some industries use the same ton units as the USA, which is 2000 lbs. https://en.wikipedia.org/wiki/Ton#Units_of_mass/weight . Where is it specified that a tonne is 2000 kg in Canada?
Franco
Milli is 1000th, as in milligram, millimeter, milliliter…all being 1000th of. As is Centi, 100th of.
Kilo is 1000 of, like kilogram, kilometer.
Franco
JoeM’s explanation of…”Centi is “Up To One Thousand Under” and Kilo is “Up To One Thousand Over.””…was a bit hard to follow, The “up to” and the “over” or “under”, was confusing, but I believe he made a mistake in saying 2000kg.
“Up To One Thousand Over”, not sure what he meant by this but 1000 meters = 1 Kilometer, 999 meters is not Kilo anything. Much less common are hectometer (100 meters) and decimeter (10 meters)
I am not sure when tonne came to be in the English vernacular. Tonne is actually the French word for ton, and when I was a kid in school (1960’s), it did not exist in English, not for weights and measurements.
A ton is 2,204 pounds. 2000 pounds is (or was) commonly referred to as a metric ton. I looked at the Oxford and Cambridge dictionary, and they do list tonne as 2000 pounds. So I guess a metric ton is used less and tonne is the new word ! (like bespoke! OMG, was custom so bad?)
jake
Thank you for starting the thread. It is interesting to understand that some units have so many different meanings in different places and contexts. I will help remind me to try hard for clarity in future communications.
Relative to weight and mass, dictionary.cambridge.org says
ton is “a unit for measuring weight. In the UK a ton is equal to 1,016 kilograms or 2,240 pounds. In the US a ton is equal to 907.18 kilograms or 2,000 pounds. A metric ton is equal to 1000 kilograms or 2,205 pounds”.
miriam-webster.com says ton is “1: any of various units of weight:”a: SHORT TON” and “b: METRIC TON”. A short ton is “a unit of weight equal to 2000 pounds”, a metric ton is “a unit of mass equal to 1000 kilograms”, and a tonne is a “METRIC TON”.
Franco
Thanks for posting this…in a previous post, I stated that a metric ton is 2000 lbs, which is clearly wrong.
Joren
This. Look at BTUs for example:
Btu—British thermal unit(s)
Ccf—the volume of 100 cubic feet (cf)
M—one thousand (1,000)
MM—one million (1,000,000)
Mcf—the volume of 1,000 cubic feet
MMBtu—1,000,000 British thermal units
Therm—One therm equals 100,000 Btu, or 0.10 MMBtu
https://www.eia.gov/tools/faqs/faq.php?id=45&t=8
Dave
Went looking to see if anyone pointed that calipers are not the best choice when one one-thousandth of either unit is important. Micrometers are. Calipers shine when a hundredth is important.
JR Ramos
Mostly agree but good quality calipers *used correctly* can be fine with a thou. Similarly, a misused mike can remove any added precision (or one that’s out of whack…or an exceptionally poor quality import although it seems most of those these days aren’t so bad). I’ve developed good trust in my Mitutoyo digital calipers but I also try to use them smartly and never forget to wipe the surfaces. There are times where the mike is just easier to use and remove from a surface and hold the reading. As these tools became cheaper and more accessible, it seems that a lot of folks use them and never receive basic instruction on using them the right way and it’s so easy with either one to introduce significant error.
Stuart
I agree.
I couldn’t think of a good image so I pulled this one from the ToolGuyd media archive.
If you’re testing to tens of mils, it’s fine. Thousandths level accuracy? Micrometers or a thickness gauge are better.
I like ratcheting thimble micrometers for repeatability.
xu lu
I’m all in on Imperial units of measure. It is the hill upon which i will choose to die. Cm, mm, liter and now mil-ugh. Fractions keep the brain sharp; so does converting to decimels and back again. No one asked but i feel the same about cursive- you stop printing in the second grade.
Stuart
Mils are an imperial unit, not metric.
Fractions can invite errors and mistakes. They can be convenient, but up to a limit.
What’s the difference if one bucket has a wall thickness of 0.070″ and the other 0.090″, expressed in a fraction? How long will it take you to do that without a calculator, compared to working with decimals? Convert 0.070″ and 0.090″ to fractions and then find the difference. How far off is the answer compared to working with decimals?
70 mil is approximately 4.48/64, and would round to 1/16.
90 mil is approximately 6.76/64, and would round to 3/32.
3/32 – 1/16 = 1/32, or 0.03125″. That’s quite a bit off from 0.020″, with an error of more than 56%. Sure, you can try to convert the number into 128ths, but is there a point to that when decimal notation is easiest? If you say 0.070 is 7/100, and 0.090 is 9/100, that’s not what I would assume you’re referring to, since that’s just the grade school version of learning to work with decimal notation for the first time.
Even if you just convert just the difference, that would be 1/64, which is off from 0.020″ by nearly 22%.
I get it – working with numbers can be fun and can keep the brain sharp. But they become impractical when accuracy is important.
Peter Coffin
If you are planning on landing a craft on Mars; do agree on the unit of measure prior to landing.
Jon
Industrial coating thickness is measured in Mils. I used to work in the petrochemical industry performing out of service inspections on above ground fuel storage tanks. Often times the tank floors are coated with either an epoxy or fiberglass lining. We measured these coatings in Mils.
Philip John
Such a pain in the arse… for laser alignment guy and his wrench partner. Or when also When talking coefficient of expansion.
Paul Davis
I first came across the measurement of “mil” in tank gunnery. Tankers adjust fire on the main gun left/right/up and down using “mils”. a description can be found on this old tank gunnery manual I found online:
http://bits.de/NRANEU/others/amd-us-archive/FM17-12C1%2861%29.pdf
page 27. Its used to describe the portion of a circle’s arc one meter in length at 1km. A tank commander may give a command after the initial round misses (a rare occurrence with an experienced gunner) such as
“over left!” “Drop one mil, right 2 mils” “Fire” If the target is ranged at 2000 meters, he is effectively saying we missed over by 2 meters and to the left by 4 meters. If the target is 3000 meters away, its 3 meters over and 6 meters left. (No tanker would ever miss at 1000 meters or less with the main gun).
Stuart
That’s a different mil.