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Taking Measure

Just a Standard Blog

Busting Myths about the Metric System

Elizabeth Gentry holding a kilogram test weight in the weights and measures training lab

Elizabeth Benham and other NIST weights and measures metrologists train weights and measures inspectors from across the country to use standard weights like this to test measurement devices like grocery store scales for accuracy.

Credit: F. Webber/NIST

This year will be the 45th anniversary of the Metric Conversion Act, which was signed on December 23, 1975, by President Gerald R. Ford. Normally, we celebrate by sharing metric education resources, but this year I want to use the occasion to dispel some common misconceptions about the U.S. relationship with the metric system.

You’ve probably heard that the United States, Liberia, and Burma (aka Myanmar) are the only countries that don’t use the metric system (International System of Units or SI). You may have even seen a map that has been incriminatingly illustrated to show how they are out of step with the rest of the world.

 

metric system adoption map
Countries that have not "officially" adopted the metric system (The United States, Myanmar, and Liberia) in gray.
Credit: AzaToth [Public domain], via Wikimedia Commons

It’s a compelling story and often repeated, but you might be surprised to learn that it’s simply untrue!

While it’s true that metric use is mandatory in some countries and voluntary in others, all countries have recognized and adopted the SI, including the United States.

Russ Rowlett, retired University of North Carolina at Chapel Hill professor of education and mathematics, emphasizes on his website that becoming metric is not a one-time event but a process that happens over time. Every international economy is positioned somewhere along a continuum moving toward increased SI use. There are still countries that are amending their national laws to adopt a mandatory metric policy and others pursuing voluntary metrication.

The United States was one of the original countries to sign the Treaty of the Meter in 1875, which is now celebrated annually on May 20, World Metrology Day. It’s been legal to use the metric system since 1866, and metric became the preferred system of weights and measures for U.S. trade and commerce in 1988.

metric continuum
Metric system use in the U.S. lies along a continuum where some measures are entirely in metric and others are entirely devoid of it, at least at the consumer level.
Credit: E. Benham/NIST

Did you know?

  • We use the SI every second of every day. After all, the second (s) is the SI base unit of time.

  • U.S. coins & currency are produced using metric specifications.
  • Many U.S. products, like wine and distilled spirits, have been successfully sold with only metric measures since the early 1980s.
  • Metric units are used extensively on packages to provide net quantity, nutrition, and health-related information, and for prescription drugs, over-the-counter medicine, vitamin supplement dosing, and other consumer products.
  • SI units are increasingly used on consumer product labeling in the U.S. lighting sector. Voluntary package labeling standards adopted by flashlight manufacturers help consumers make product comparisons. While shopping, consumers easily evaluate light output (lumen), peak beam intensity (candela), beam distance (meter), and impact resistance (meter).

It’s impossible to avoid using the metric system in the United States. All our measurement units, including U.S. customary units you’re familiar with (feet, pounds, gallons, Fahrenheit, etc.), are defined in terms of the SI—and mass, length, and volume have been defined in metric units since 1893! The SI’s influence is pervasive and felt even if most people don’t know it. I envision U.S. metric practice like a huge iceberg. Above the water’s surface, U.S. customary units appear to still be in full effect. In actuality, below the water’s surface, we find that all measurements are dependent on the SI, linked through an unbroken chain of traceable measurements.

metric iceberg showing SI below the surface and customary measurements above the water line.
The U.S. measurement infrastructure depends on the SI.
Credit: E. Benham/NIST

Although U.S. customary units are still seen alongside metric units on product labels and merchandise literature, it’s common for the goods themselves to be made using SI-based manufacturing processes. Why? While some businesses are concerned that consumers expect to see customary units on the package, when it comes to manufacturing processes, they are under constant pressure to stay competitive. Adopting the latest science and technology, developed using metric design practices, enables innovation. In addition, many industries extensively use international supply lines to develop, manufacture and sell their products around the world.

I’m the coordinator of NIST’s Metric Program. Because of my passion for all things metric, I encourage companies to investigate adopting metric practices whenever possible and show them how doing so can make a strategic economic impact for their organization. Changes in technology and extremely competitive domestic and global marketplaces can compel businesses with little previous experience to explore metric use. Many have found that going metric pays off, resulting in a competitive advantage.

Going metric pays off

During the recent recession, lumber companies located in the U.S. Northwest saw their U.S. customer base shrink, but their Canadian and Japanese markets, both of which use metric, expand—especially after the 2011 earthquake and tsunami. Wood-product producers made adjustments so that their production systems could flex between metric and U.S. customary measures based on what their customers needed. Because so much of the world uses metric only, more and more U.S. companies are recognizing the benefits of metric as they find new international markets for their products.

If your business is considering making the switch to metric, I would encourage you to conduct small beta tests to explore how your customers react. Research can help ensure decisions aren’t based on out-of-date information or preconceived notions. You might be pleasantly surprised by how quickly customers adapt—and how using metric benefits the bottom line.

And as always, if you need advice, be sure to give NIST a call. We’re here to help!

*Editor's note: This post was updated on October 6, 2020, to include information about units of measure for lighting, to include a new "metric continuum" graphic, and to make other minor changes. It was originally published on December 23, 2016.

 

About the author

Elizabeth Benham

Since becoming Metric Coordinator in 2005, Elizabeth has worked to support voluntary conversion to the International System of Units (SI), commonly known as the metric system, in the U.S. In addition...

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Comments

I grew up in Europe with the metric system and only used imperial units for floppy disks and monitor sizes. Everything else is metric.

Moved to the USA as an adult and after an adjustment period I like the imperial system a lot better.
The reasons are much in line with Mr Michael Gorsich above. When you have a base 12 or 16 it is much easier to calculate fractions. Look at the number of wrenches and the number of different threads in the metric system. Compare to the SAE standards. The SAE standards are much more practical.

The imperial measurement system is comprised of units that everyday people found useful for their everyday use.
The French metric system is comprised of units scientists in a lab decided on and forced everybody else to use.

The difference is in crowdsourcing vs central planning.

In the crowdsourcing model there are a number of different ideas. Since it is impracticable for everybody to use different solutions, there is a natural selection and only the most popular ideas prevail. You can see this in the imperial system - there were originally a lot more units of measurement, most of which have been deprecated.

In the central planning model there is one decisionmaker, which can be a single person or a committee, and everybody else will be forced to "agree to disagree".

The central planning method often comes up with higher levels of organization, elegancy, consistency. The crowdsourcing model often has more taylored solutions, moe choices, but more chaotic.
Think of "master-planned" neighborhoods vs an old country lane.
Think of communism vs free enterprise.

Do you prefer freedom or control?

It is no surprise that a government agency would favor control. But it's not just the government. Most people these days favor control over freedom. That's why we have things like HomeOwners Associations. People want every last piece of grass controlled. We have air conditioning, heat, humidifiers, dehumidifiers, every aspect of most people's environment is tightly controlled.

We've created a world where control, conformity,egality is expected, respected, normalized.
Freedom and diversity is loathed and dismissed as simplistic, uneducated, primitive.

Embrace diversity. Dare to be different. Let the rest of the world turn into Borg drones if they so desire. We go our own way.

Oh, I don't know - I could be wrong, there are a few things science has done to advance civilization and make it better. I'm not sure why a cohesive, rational, interrelated and universally acknowledged system of measure wouldn't qualify as well. I also don't understand why the USA defends its use of the arcane now as its own proprietary "system" but at some point, the rest of world favored its use and they seemed to be ok with being part of that. Also, if a working knowledge and practical use of the SI is solely Americas "elite" scientists and engineers, how is that helping when every other third grader everywhere else on earth is proficient in its use? Advocates of a metric US are typically referred to as "metric snobs". My definition of snobbery is the expectation that everybody else provide you your own special units, in your own special "system." The metric system is an UPGRADE. It's not a threat to liberty, it's not a globalist plot. It's an UPGRADE. Quit being paranoid.

I suggest all correspondents read the following document.

Going Metric: An Analysis of Experiences in Five Nations and ...https://files.eric.ed.gov › fulltext
PDF
by AB Chalupsky · 1974 — Industrial Training Advisory Committee of the Australian Metric Conversion. Board; and ... National Bureau of Standards and the information provided by Mr. Louis. Barbrow ... problems in metric education are identified and coping strategies-are ... The White Paper is generally cautious and claims for success are quali- fied.
140 pages

With climate change being such a 'hot' topic right now, in order to fully take part in international discussions, it would make sense if the USA at least used the same unit of temperature as the rest of the world!
Looking at the broader issue of measurement, I find it so strange that whilst America has advanced science and technology in so many areas but yet their political leaders have lacked the foresight to fully change to metric which would make international trade and the exchange of information so much easier for them.
Unfortunately, polititions, probably due to their education are often scientifically illiterate and don't appreciate the benifits that full metrication would bring to the USA.
Whist the people of the world may speak many languages, they all (apart from the US) measure things in the same language.

Tim, you said,

"With climate change being such a 'hot' topic right now, in order to fully take part in international discussions, it would make sense if the USA at least used the same unit of temperature as the rest of the world!"

We do. Just not in daily life. An American scientist absolutely understands what 20 degrees centigrade indicates. But the announcements on TV are done in Fahrenheit because it's a free country and that's their choice as individuals. It is certainly not illegal for a TV or radio station to start announcing the temperature in degrees centigrade. To my knowledge there's nothing illegal about announcements made in Fahrenheit in Italy, either, for the same reason.

And I think you'll find that the Americans dominate climate science just like we dominate every other form of human endeavor. Don't mistake the opinions of politicians for the facts of science which are universal, in all countries.

This article trying to explain "levels of adoption" and how "it takes time" to adopt the SI made me laugh. Of course 140+ years is not enough to sink in.

Some of the most brilliant minds and inventions came from the US, but the average Joe is not capable of adapt to SI.

Of course some countries still use a few imperial measurements, but the absolute majority of daily life things are SI, like distance (meters), weight (grams), volume (liters) or temperature (celsius).

Of course the US product packages come with both measures, otherwise it's hard to export it, since no one else will understand it.

Also, the US uses imperial to guide the size of their packaging. E.g. you sell vegetables in 2 lbs packages, which in SI is a weird total of 907g, instead of customary 1kg. Same for bottles, instead of 1 liter, 1.something which is equivalent to something else in fluid ounces. BTW, what the heck is a fluid ounce? Why would you measure things in eighths of an inch? Do you love fractions that much?

The funniest thing of all, is that the US were the first to be independent from UK (compared to Australia, Canada, etc) but you can't get rid of their weird system, which even UK ditched.

Hally blinkin' lujah! The Imperial system is utter tosh. We, the Brits, are ultimately responsible for inflicting this on the world for the longest. Difference is, in our shame, we know it's useless and have been big enough to dump it. Whereas instead of admitting they've been dumped-on and calling it British or Imperial - this to at least shift the rightful blame, Americans actually call the whole mess 'American'.

With all due respect, it's really not using the metric system when you continue teaching and measuring things with the imperial system. Defining the imperial system using the metric system isn't using the metric system. Please become practically metric.

When observing and quantifying the world around you, pounds and inches just won't do! Kilogrammes and metres are much more scalable, from chemistry to physics.

It's not a myth. When I buy gasoline in the USA I do not pay per liter, I pay per gallon. When I drive, all the signs are written in miles, not kilometers. When I get close to an exit, it says 1/2 mile, 1/4 mile, etc., not 400m or 200m. But when I am in Europe, the gasoline is priced in euros per liter and the signs are all in kilometers.

A couple points that I don't think have been brought up yet.

a) Nobody outside of the USA calls the SI (ISU) the "metric system". The term "metric system" is just a generic term for "system of units of measurement". It's totally valid to call British Imperial units a "metric system" - since "metric system" does not refer to any one system of measurement.

b) One huge benefit of the SI is that it really does make teaching the sciences easier. British Imperial units predates Newton's Laws! There would likely be a marked improvement in US educational attainment in science as a direct result of adopting the SI. And if that fails to sway people you can just tell them "Using SI means never having to worry about slug feet!"

I worked in scientific circles for many years, and worked for a while with my wife teaching her elementary students math and science.

When I taught her students measurements, I eventually found that the easiest way to get to them was to ask how many ways to measure length in our old-fashioned system, then how many ways in metric. It was shocking to them that there are many different measures of length in the old way (inch, foot, yard, rod, etc.), but only one in the metric system (meter). And nearly all the other measures are just a simple. Yes, I did have to explain that "kilo" means one thousand, "centi" means one hundredth, etc.

Unfortunately, even the teachers are hung up on the silly old-fashioned measurements, and regard the familiar as "easy", and the metric as "hard". Unless we get the educators to accept education, we are unlikely to make good headway in metrication.

The Imperial system is utter tosh. We, the Brits, are ultimately responsible for inflicting this on the world for the longest. Difference is, in our shame, we know it's useless and have been big enough to dump it. Whereas instead of admitting they've been dumped-on and calling it British or Imperial - this to at least shift the rightful blame, Americans actually call the whole mess 'American'.

One of the criticisms of the metric system is its lack of "human scale" quantities. However these critics have missed the fact that metric does have its own "human" scales - but based on metric not conversions from imperial/USCU. So a piece of 2x4 timber is now 50x100, the difference is so small that it would be indistinguishable.

A 1 lb jar of peanut butter is 500g (1.1 lb)
A quart of milk is 1 litre (2.11 pints)
A 2 lb bag of flour is 1 kg (2.2 lb)
A 50 lb bag of cement is now 20 or 25 kg (44 or 55.1 lb).
A 1/4 (0.25) acre section (plot) is 1,000 m^2 (or 10 ares) (0.247 acres)
A speed limit of 30 mph is 50kph (31.25 mph).
A tall man (6') is 1.80m (5'11").

And the metric system is so much better than imperial/USCU in calculations that it's out of the park.

Which is the bigger screw/drill : 3/8", 5/16", 25/65". Or in metric 0.38, 0.31 or 0.39mm?
How much water do you need for an aquarium 36"w, 18"h and 15"d? That would be quicker to convert to metric, do the calculation and convert the answer back to USCU! And the metric system would give you the volume AND the weight! What is the weight of the above in lb? Don't make the mistake of "a pint's a pound the world around"! A US pint does NOT weigh a pound - it weighs 1.04 lb! (because the weight/volume link in USCU is based on wine, not water).

The metric and imperial systems are like languages. If you constantly translate you'll get funny translations, but if you work in one or the other and accept their own idiosyncrasies, they both work, sort of. But metric has the considerable advantage of
- ease of calculation,
- consistencies of units within a parameter (12" = 1', 3' = 1yd, 1,760yds = 1 mile; 14 oz = 1 lb etc.), in metric it's all based on 1000s, and 10s and 100s for day to day use.
- interlinkage between parameters (1,000 ml or 1 litre of water weighs 1,000 g or 1kg)

Full disclosure - I have lived in the UK (imperial at the time), Europe and New Zealand (metric). I consider myself "bi-lingual" and can use both systems (though it's imperial and not USCU).

They even refuse to spell it the correct way. It's metre and not meter. Article refers to Treaty of the Meter, which, of course links to the correct name, Treaty of the Metre.

One of the advantages of using the International System of Units (SI) is that written technical information can be effectively communicated to overcome the variations of language – including spelling. SI unit symbols are the best way to communicate across all languages and national writing practices. For example, international scientists report length quantity data using the SI base unit symbol “m,” however they may spell the measurement unit differently when writing a sentence (e.g., “metro” – Spanish, “metre” – British English, or “meter” – American English).

The International Bureau of Weights and Measures (BIPM) SI Brochure (https://www.bipm.org/en/publications/si-brochure) has long recognized that “small spelling variations occur in the language of English-speaking countries (for instance, “metre” and “meter,” litre” and “liter”).” French is the primary language of the SI Brochure. Within the secondary English language section, British English spelling is used according to ISO style guidance (https://www.iso.org/ISO-house-style.html) that applies Oxford English Dictionary spelling.

In order to help U.S. industry use the SI as broadly as possible our publications, like NSIT Special Publication (SP) 330 (https://www.nist.gov/pml/special-publication-330) and this blog article, are written for an American audience according to the United States Government Printing Office Style Manual (https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2016/pdf/GPO-STYLEM…) that applies Webster's Third New International Dictionary spelling.

I spent five years in England, from the age of 2 to 7. So I started to learn with imperial units. Then I moved back to France and then educated to the metric system.
I work now as engineer in a global company, leader in rolling bearings, working with application engineers all other the world. I deal with imperial units about 5% of my working time.

I have metric and imperial spanners for my Land Rover since bolts are a mix of metric and imperial threads. On the rear dampers, the upper thread is metric, the lower is imperial...... for about the same diameter. So I screwed the wrong nut damaging the thread.

For a mechanical engineer point of view, metric or imperial, one isn't better than the other.
It is just that people used to one system, are so familiar with it that the other system looks awkward.

The issue is that the two exist, creating problems like the NASA loosing 327 million dollars Mars climate Orbiter in 1999...... or making me damage the thread of a damper on my Land Rover.

To avoid problems we should all have the same way of measuring.
Like language. In the company in which I work, it was decided that the international language should be English. Because in our world it is the business language. And which English ? The one used in the ISO standard : Oxford English.

So what is the most used today measurement system : the metric. Then we should all go to metric.

Now is the metric french ?
The word isn't, and was already used as measurement unit long time before the french revolution. It is a Greek word (metreo), and first time used as a unit, by an Italian in 1675.
There as been several metre, with different lengths.

The french just wanted to create units of length, mass and volume that would be the same in all french regions. A pint (also old unit in France) of milk could have different volume in two different towns, such as Paris and Lyon. The units should not rely on a dimension that could change, like the length of the king's foot.

It was decided to use the name metre, because in greek it meant "to measure" and to use part of the circumference of the earth as length of the unit (one ten-millionth of the distance from the equator to the North Pole along a great circle).

It was seen as a new universal system, based on scientific dimensions, making manufacturing and commercial exchanges easier, since replacing all local units and that's why it spread.

Note that the Prussians won the war against the French in 1870, but they adopted the metric system in 1872.

To sum up:

Metric or imperial, none is better than the other.

People prefer one system because they are familiar with it.

The use of two (or more) measuring system creates issues. It is better to have one common one, like the language.

The metric system is now used by too many countries. For manufacturing and commercial international exchanges, better go all to metric.

> "creating problems like the NASA loosing 327 million dollars Mars climate Orbiter in 1999"
The problem I have with this argument is that it's literally the ONLY argument people can make about why the US customary and Metric systems are incompatible. And if one example is enough to discredit something (which it isn't) then I have plenty of single examples of countries having non-SI units in wide-enough use for it to be considered a non-metric country. But obviously having one example is not enough to prove a point.

On an international scale, the US is plenty metricized, especially for science and military purposes (like NATO standards). The key distinction lies at the local level: people tend to use the system they're most familiar with, just as many other nations have their traditional, non-SI units for specific purposes, such as 'vara' in Spanish-speaking countries or 'pyeong' in South Korea. Even powerful countries like India still utilize inches for certain applications.

If the US weren't a global superpower, the situation might be different. Non-superpower status would likely entail significant imports in metric units, promoting conversion. Historically, this has been the case, prompting the US government to make the metric system official in the 19th century due to the power and influence of the French state (afterall, that's where the metric system originated from!). However, the reality is the reverse: the US is a global superpower, and US Customary units have influenced global markets, with products often sold in inches, feet, etc. The US lacks incentives to convert units for international sales, given its global dominance, at least beyond maintaining good relationships with their international partners.

Sure it would be nice to have a single unit worldwide... but it would also be nice if everyone spoke the same language, used the same money, had the same values, etc. However, practical complexities arise. While some principles like 'murder is wrong' find universal consensus, stuff like unit systems and languages lack straightforward solutions, which, as you've noted: "Metric or imperial, none is better than the other." Change typically necessitates compelling incentives.

You brought up language dynamics. French once dominated international diplomacy, reflecting French power in the 17th-19th centuries, leading US leaders to embrace the French language as well as adoption of the French-founded metric system in the 19th century. However, the 20th and 21st centuries witnessed English's ascendancy as the global language, due to the British Empire's influence and later, the United States. And yet in spite of this change, the French continue to speak French locally. How is this any different than Americans continuing to use US Customary units locally despite international norms? Both prefer non-international standards locally and will resist change as they reject the "but the rest of the world is doing it!" argument. Nevertheless, both nations WILL shift to international norms, but only when necessary, namely French nationals speaking in English for global travel or Americans using the Metric system for international commerce and military needs.

So until a compelling reason arises for nations to adopt international standards universally, both domestically and abroad, such differences will persist, and they will continue to create issues for the forseeable future. For example, just as US/UK units being an issue in this metric world if you want to but a part for a US/UK brand of automobile that was sold in the EU (even tho those US/UK parts were intended for domestic US/UK mechanics), French will be an issue in this English world if I want to, say, buy a book on French history (even tho those French books were intended for domestic French readers)... as both circumstances will still require time, energy and especially money to convert/translate between the two. Should I criticize the French writer of a book intended for French readers for not considering writing their book in the internationally standard language of English?

I'm from a third-world country (let's call it District 13 from the Hunger Games trilogy). I have a US-based online client that I regularly interact with - she insists I send all commonly available data in US customary units. Now feet is something I'm used to (we all know what a six-foot person is like) but not when it is used to convey parking distances (I just can't visualize 200 feet the way I do 66 meters. We all know an initial Olympic sprint is 100 meters.) Yards are a better metric as it's just 3x feet, or slightly less than a meter. So, 200 yards ~ 200 meters is about the same thing. I find pounds and ounces pretty difficult to relate with, although 1 KG = 2.2 lbs is understandable, but if I have to buy something online, and it is listed in lbs and ounces, I feel a bit shortchanged. I ordered whey powder the other day and it said 4 lb 2 oz, sounds like a big deal when you read it that way but it's just around 2 Kg, which feels like a rip-off because we get 5 kg whey powder at the same price. I know gallons (3.7 liters) but pints are impossible to relate - but yes, I do know about ordering a British pint at a bar ~ 568 ml. Still worldwide (outside the US) everyone orders beer in 330 ml and above. The most difficult measurements to me are pounds per square inch (PSI) and Horse powers. Don't know what the heck they are. Peaceout, homies.

What gets me is the reverse: how many countries still use their own non-SI (or non-SI-based) units? In my experience, it's largely all of them, albeit in different ways.

First off it's rather rude to hear Brits complain about American use of Customary Units ("I learned it from YOU, Dad!!"), seeing as they still use pints, feets-and-inches, miles, etc. Then there's also a level of Americanization where stuff like HDTVs and cellphone screens are described in inches worldwide; IIRC "pulgadas" are used in Spanish-speaking countries instead of the word "inches", while Germans use "fuß" for feet with stuff like fabric.

But for the rest... Some still use non-SI terms due to tradition even though by now it's been converted to an SI-related equivilent, such as the German "Pfund", which is defined as 500 grams, or the widly used "hectare" which is 100m x 100m. Sometimes a country will have one straight-up single non-SI unit, like the "pyeong" which is a measurement of floor space for the purposes of real estate in South Korea, or the use of "vara" in Spanish-speaking countries which is a length of about 0.835905 meters. And then for others, it's more with the older generation who grew up in a non-metric world and still use them privately, but younger generations aren't too keen on using them; sometimes it's the aforementioned "vara", depending on the country and context.

Given the use of non-SI and non-SI based units, this leads me to believe that metrification in the US is not much different than the rest of the world, the difference is just a matter of what degree. For example, if an inch is strictly defined as 2.54 cm, how is that different than the German Pfund which is defined as 500 grams? Both are non-SI units albeit ones that use the SI as a base, and both probably won't be used in an official scientific paper... would they? But yeah, the map showing the US, Liberia and Myanmar/Burma as the ONLY non-SI nations is ignorant at best and deceptively disingenuous at worst.

Online shopping metrified? Let's see go to Amazon USA and search olive oil. They will give price per pound, or per ounce or per pt whatever that is. Have fun comparing.

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