# What is the purpose of the US customary system of measurement? **URL:** \ **Category:** Factual Questions\ **Created:** [May 31, 2013, 1:57pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784 "2013-05-31T13:57:03Z")\ **Posts on this page:** 20\ **Page:** 12
**Author:** ![Mogle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mogle/32/12021_2.png) [@Mogle](https://boards.straightdope.com/u/Mogle)\ **Post date:** [June 2, 2013, 10:46am UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/221 "2013-06-02T10:46:05Z")
> [@DrDeth](#): > > For that F is superior. Weather forecasters almost never need to use negative numbers. And, if they’d left it alone, Body temp would be 100. See Fahrenheit picked what he thought was the best two numbers for 0 and 100- body temp and the coldest you can get a ice & salt water mix. The [Master](http://www.straightdope.com/columns/read/845/on-the-fahrenheit-scale-why-is-32-freezing-and-212-boiling) disagree, 100 means nothing and never meant anything on the Fahrenheit scale, Fahrenheit picked 96°F as body temperature. 0°F is colder than it ever gets in Denmark because the Dane that inspired Fahrenheit didn’t like negative numbers. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [June 2, 2013, 1:08pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/222 "2013-06-02T13:08:42Z")
> [@DCnDC](#): > > I’ll give you the answer if you can give me a legitimate, practical, everyman reason why I would need to know that. Your land perimeter is 2.567 km. Fencing comes in 8 feet wide [panels](http://www.homedepot.com/h_d1/N-5yc1vZc3pk/h_d2/Navigation?catalogId=10053&langId=-1&storeId=10051). Panels are separated by 2x4s. You want to add 4 42" wide gates. How many panels should you buy? But the real reason is: if imperial units are so good, why can’t people use them exclusively? Why do they still resort to decimal points? ---
**Author:** ![lance\_strongarm](https://avatars.discourse-cdn.com/v4/letter/l/87869e/32.png) [@lance\_strongarm](https://boards.straightdope.com/u/lance_strongarm)\ **Post date:** [June 2, 2013, 2:28pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/223 "2013-06-02T14:28:55Z")
> [@SCAdian](#): > > Can’t be that difficult - little kids do it all the time! And then they promptly forget them. What a waste of time to teach kids something they shouldn’t need to know in the first place. ---
**Author:** ![Smapti](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smapti/32/17938_2.png) [@Smapti](https://boards.straightdope.com/u/Smapti)\ **Post date:** [June 2, 2013, 3:22pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/224 "2013-06-02T15:22:04Z")
> [@AaronX](#): > > But the real reason is: if imperial units are so good, why can’t people use them exclusively? Why do they still resort to decimal points? If metric units are so good, why can’t people use them exclusively? Why would you say 2.567 km instead of 2 km, 5 hm, 6 dam, 7 m? But to answer your real question - I’d hire a contractor and let him deal with buying panels. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [June 2, 2013, 3:46pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/225 "2013-06-02T15:46:31Z")
> [@pulykamell](#): > > I meant 16 tbsp in a cup. Wet or dry? ---
**Author:** ![R3d\_Anonymous](https://avatars.discourse-cdn.com/v4/letter/r/aeb1de/32.png) [@R3d\_Anonymous](https://boards.straightdope.com/u/R3d_Anonymous)\ **Post date:** [June 2, 2013, 3:58pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/226 "2013-06-02T15:58:13Z")
> [@DrDeth](#): > > Let me introduce you to the concept of “SigFigs”. What is the purpose of significant figures? I have never understood. Nearly everyone including me asked the same question when we were learning them in the beginning of this year. Why not just give the most precise answer? ---
**Author:** ![Glazer](https://avatars.discourse-cdn.com/v4/letter/g/a88e57/32.png) [@Glazer](https://boards.straightdope.com/u/Glazer)\ **Post date:** [June 2, 2013, 4:01pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/227 "2013-06-02T16:01:34Z")
> [@Anonymous User](#): > > What makes more sense or at least seems more intuitive (rhetorical question)? 0°C and 100°C being the freezing and boiling points or 32°F and 212°F? Fahrenheit makes perfect sense outside of the lab. With 0[sup]o[/sup]F. and 100[sup]o[/sup]F being the range of temperatures we have to deal with throughout the year. ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [June 2, 2013, 4:09pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/228 "2013-06-02T16:09:20Z")
> [@Anonymous User](#): > > What is the purpose of significant figures? I have never understood. Nearly everyone including me asked the same question when we were learning them in the beginning of this year. Why not just give the most precise answer? Define “most precise.” If you weigh yourself as 144.832 pounds, but the scales have a typical error of a half-pound or so it makes more sense to just round to 145 pounds. Writing “144.8 pounds” might not be wrong – 144.8 may be a better estimate than 145.0, but to write 144.83 would be misleading: it would imply an accuracy that isn’t there. They’re laughing at me for asking about the 2-parts-per-million difference between the U.S. statutory inch and the international inch because no surveyor gets anywhere near enough accuracy to matter. Physicists do experiments with more accuracy than that but, getting back to thread subject, _always do such measurements in the metric system_, I think. ---
**Author:** ![fumster](https://avatars.discourse-cdn.com/v4/letter/f/e9c0ed/32.png) [@fumster](https://boards.straightdope.com/u/fumster)\ **Post date:** [June 2, 2013, 4:32pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/229 "2013-06-02T16:32:29Z")
> [@DrDeth](#): > > Those first two are The Weather, right? And for the weather, it’s best not having to use negative numbers. First, that is an assertion without any reasoning behind it. Second, it gets below zero Fahrenheit on a regular basis in many parts of the country. > [@](#): > > And gosh, you can’t do that once? Of course, but why have to look up the freezing point of water. In centigrade it’s easy to remember. > [@](#): > > For purposes of everyday weather F is better than C. No it’s not. C is better: I can instantly know if it is below freezing. Something I care about even in mild Oregon because of the danger of black ice. > [@](#): > > And, let me emphasize this again. Neither is “more scientific” or “more metric”. There’s a hundred degrees in F also, just between different points. You are right, the fact that there is a 100 degrees between freezing and cooling does not make it more scientific. But the metric system as a whole is more suited for technical purposes. One example: a calorie is the energy needed to raise the temperature of 1 gram of water through 1 °C. Whether or not is is “worth it” to change to the metric system is open to debate. The idea that the American system is “better” in any manner is not. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [June 2, 2013, 5:05pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/230 "2013-06-02T17:05:30Z")
> [@Glazer](#): > > Fahrenheit makes perfect sense outside of the lab. With 0[sup]o[/sup]F. and 100[sup]o[/sup]F being the range of temperatures we have to deal with throughout the year. That’s a very narrow perspective, and of course it is not true of most of the world, including a large percentage of the human population. If Fahrenheit had been Panamanian, Brazilian, or South Indian, what’s 50 F now would be 0 degrees. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [June 2, 2013, 5:08pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/231 "2013-06-02T17:08:24Z")
> [@Martin\_Hyde](#): > > Well I know it’s a fun story but the Mars Climate Orbiter failure is really a pretty poor example when responding to my claim that most people in their day-to-day lives would realize few if any of the benefits of a change. I imagine vanishingly few people on the forums here are involved in the design of NASA vehicles (maybe 1-2 might be, maybe.) The point isn’t that the failure of the Mars Climate Orbiter personally impacted all but a tiny minority of US citizens (other than the loss of a $700 million mission paid for by the taxpayers) but that _in order to accommodate the desire to use US customary units used by the US population_ the mission was lost. I would agree that for most people who are not engineers, scientists, or technicians and who do not perform algebraic operations more complex than dividing by 4, the choice of system of measurement is essentially arbitrary. But to argue that the US customary system is “more intuitive”, “easier to use”, “too hard to get away from” are equivocations without factual basis. We could, in fact, convert from customary to SI with only a modest amount of pain, and in fact the greatest impact would be on the same engineers and technicians who use materials and tooling that are designed for US customary units and SAE fastener sizes. > [@Martin\_Hyde](#): > > But I think there’s probably a bigger reason than just building codes that most of the construction trade still works with customary units–because it doesn’t appear that metric is intrinsically that advantageous in that industry. Actually, the construction industry (or at least, segments of it) have tried to go to decimal feet–essentially a hybrid “metric” conversion–several times, but due to the fact that codes and materials specify dimensions in a combination of inches and feet has made this problematic despite the conversion errors that inevitably crop up. Part of the problem in the natural migration to the system of measurement used by the rest of the world is that standards and regulations are even slower to change than industries. Stranger ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [June 2, 2013, 6:26pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/232 "2013-06-02T18:26:45Z")
> [@fumster](#): > > Of course, but why have to look up the freezing point of water. In centigrade it’s easy to remember. > > No it’s not. C is better: I can instantly know if it is below freezing. Something I care about even in mild Oregon because of the danger of black ice. > . Sure it is. But many other temps are not such round numbers. You can “instantly” know with F, too. In C you have to remember that 0 is freezing, in F 32 is freezing. In both cases you need to know a number. There is no superiority of C over F. ---
**Author:** ![Emtar\_KronJonDerSohn](https://avatars.discourse-cdn.com/v4/letter/e/58956e/32.png) [@Emtar\_KronJonDerSohn](https://boards.straightdope.com/u/Emtar_KronJonDerSohn)\ **Post date:** [June 2, 2013, 6:29pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/233 "2013-06-02T18:29:05Z")
> [@Chronos](#): > > OK, that would be a great argument for keeping metric. What’s your argument for instead keeping a system that most people _don’t_ understand? > > For those who don’t think conversions actually come up that often, I can give a few examples: > > 1: You have a rectangular fish tank, and you want to know its volume. OK, so you get out your yardstick, and measure its length, width, and height, and multiply them. But that’s its volume in cubic inches-- How many gallons is that? > > 2: You have a recipe for cookies or brownies or something that you really like. A lot of the ingredients are measured in teaspoons or tablespoons. But that’s only for a single batch. There’s a bake sale coming up, and you want to make a whole bunch of batches. It’s too inconvenient to measure out all of those things in tablespoons, so you want to measure using cups instead. How many tablespoons are in a cup? > > 3: You’re training for a marathon by running on the track at your local gym. The track is 200 yards long. How many laps around the track do you need for a mile? > > 4: You’re interested in buying a vacant lot. You know how many feet long and wide the lot is. What is that in acres? > > 5: (bonus question) You go to Ireland and stay in a bed and breakfast. They serve a really good bread at breakfast, and you ask for the recipe. The recipe is measured in quarts, teaspoons, and tablespoons. What is that in quarts, teaspoons, and tablespoons? (this one actually happened to me) > > Can anyone in this thread who’s a fan of the American system answer all of these questions? Better yet, can you answer them without a calculator? Because if we were using the metric system, most people would be able to answer all of the equivalent questions, in their head. 1. I know from calculating the volume of my pool that approx 7.5 cubic feet = 1 gallon. 144 cubic inches = 1 cubic foot. Therefore approx 1180 cubic inches = 1 gallon. 2. A 1/4lb stick of butter is half a cup and has 8 tablespoons, so 16. 3. A standard track is 1/4 mile, not 200 yards. IF your gym has a shitty miniature 200 yard track that’s 600 feet. A mile is 5280 feet. 600x8=4800, 5280-4800=480, 480/600=.8, so 8.8 laps on the shitty miniature non standard running track = 1 mile. 4. There are approximately 43,500 sq ft in an acre. Use a real estate agent and purchase title insurance. 5. Screw Ireland and their stupid imperial quarts and such. Aren’t there 5 quarts in a gallon? I don’t know (or care to learn) how they treat tablespoons and teaspoons. So if you stay away from overseas counterfeit standard measures you’re fine. ---
**Author:** ![R3d\_Anonymous](https://avatars.discourse-cdn.com/v4/letter/r/aeb1de/32.png) [@R3d\_Anonymous](https://boards.straightdope.com/u/R3d_Anonymous)\ **Post date:** [June 2, 2013, 6:37pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/234 "2013-06-02T18:37:56Z")
> [@DrDeth](#): > > In both cases you need to know a number Yes, and that number in Celsius makes more sense and seems less arbitrary. However, I would agree that Celsius isn’t all that advantageous, but I would say that it _is_ slightly better than Fahrenheit. But then again, real men use Kelvin. 😃 (Just Kidding) ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [June 2, 2013, 6:52pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/235 "2013-06-02T18:52:29Z")
> [@Anonymous User](#): > > Yes, and that number in Celsius makes more sense and seems less arbitrary. basing it on the boiling and freezing points of water is entirely arbitrary. whether it’s less or more arbitrary than anything else is irrelevant. If we wanted something with a non-arbitrary basis we’d be using Kelvin or Rankine. > [@](#): > > However, I would agree that Celsius isn’t all that advantageous, but I would say that it _is_ slightly better than Fahrenheit. got anything better than “because I think so?” ---
**Author:** ![DCnDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dcndc/32/2842_2.png) [@DCnDC](https://boards.straightdope.com/u/DCnDC)\ **Post date:** [June 2, 2013, 8:37pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/236 "2013-06-02T20:37:27Z")
> [@Emtar\_KronJonDerSohn](#): > > 1. I know from calculating the volume of my pool that approx 7.5 cubic feet = 1 gallon. 144 cubic inches = 1 cubic foot. Therefore approx 1180 cubic inches = 1 gallon. You got that the wrong way around. there are about 7.5 gallons in a cubic foot. There are 1728 cubic inches in a cubic foot, so a gallon is 231 cubic inches. ---
**Author:** ![OldOlds](https://avatars.discourse-cdn.com/v4/letter/o/a3d4f5/32.png) [@OldOlds](https://boards.straightdope.com/u/OldOlds)\ **Post date:** [June 2, 2013, 11:52pm UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/237 "2013-06-02T23:52:48Z")
I guess I’ll weigh in… I have spent my entire career in pharmaceuticals, both manufacturing and R&D. I can tell you that I and all my colleagues know the metric system. We use it every day, and we are familiar with how “big” things are. I would say that most of us would agree it is a “better” system. However, and I think this goes to the point of some here, when we chat about the weather or give directions to each other, or if we’re complaining about needing to lose some weight, we’re NOT using the metric system. We’re just used to the old system. ---
**Author:** ![lance\_strongarm](https://avatars.discourse-cdn.com/v4/letter/l/87869e/32.png) [@lance\_strongarm](https://boards.straightdope.com/u/lance_strongarm)\ **Post date:** [June 3, 2013, 1:20am UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/238 "2013-06-03T01:20:02Z")
> [@Martin\_Hyde](#): > > I also still find it weird someone mentioned the division of the dollar into one hundred cents as an argument for the metric system. The way you divide your currency is basically independent of how you measure things. So? I mentioned it simply because our currency system makes sense and is easy to use because it’s decimal. ---
**Author:** ![lance\_strongarm](https://avatars.discourse-cdn.com/v4/letter/l/87869e/32.png) [@lance\_strongarm](https://boards.straightdope.com/u/lance_strongarm)\ **Post date:** [June 3, 2013, 1:21am UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/239 "2013-06-03T01:21:57Z")
> [@DCnDC](#): > > You got that the wrong way around. there are about 7.5 gallons in a cubic foot. There are 1728 cubic inches in a cubic foot, so a gallon is 231 cubic inches. Uh-oh, you and he keep making mistakes. I don’t even have to know any conversion factors or use a calculator to know that there are, for instance, 1000 liters in a cubic meter. ---
**Author:** ![DCnDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dcndc/32/2842_2.png) [@DCnDC](https://boards.straightdope.com/u/DCnDC)\ **Post date:** [June 3, 2013, 2:07am UTC](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784/240 "2013-06-03T02:07:21Z")
> [@lance\_strongarm](#): > > Uh-oh, you and he keep making mistakes. > > I don’t even have to know any conversion factors or use a calculator to know that there are, for instance, 1000 liters in a cubic meter. #1 I didn’t make any mistakes. #2 Once again, you’ve misinterpreted what was said. **Emtar KronJonDerSohn** ’s mistake was not a matter of the measurement system or arithmetic, it was a mix-up of units. Replace “gallons” and “feet” with “liters” and “meters” and his mistake would be identical. [Previous page](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784.md?page=11) [Next page](https://boards.straightdope.com/t/what-is-the-purpose-of-the-us-customary-system-of-measurement/659784.md?page=13)