The question in the title of the article asks which countries use the metric system — more accurately called the International System of Units — but it would be much easier to list which countries don’t use it. There are only three: Myanmar (or Burma), Liberia and the United States. Every other country in the world has adopted the metric system as the primary unit of measurement. How did this one system become so widely adopted? And why are there countries that are holdouts? We explore these questions below!
How Are Measurement Systems Created And Defined?
As humans began building more complex things, a measurement system became necessary. Often, these measurements would be based on the human body. The Ancient Egyptians, for example, used cubits that were about 52.4 centimeters, and which were roughly based on the length of a human forearm. But basing measurements on the body can only take you so far, considering each body is a different size. This would be solved by creating measuring sticks and other units with which to measure.
The British Imperial System, which evolved into the United States customary unit system Americans use today, was similarly based on fairly arbitrary measurements. It comes from the measuring done by Romans, Celts and Anglo-Saxons beginning over one thousand years ago. For one, how large a foot or an inch were started out being vastly different depending on where you were because it was hard to establish a standard. There were various royal efforts, from a 10th century Saxon king keeping a bushel measure to a proliferation of “physical embodiments” passed across England by Queen Elizabeth I. It would be like if the president handed out yardsticks to everyone so everyone’s “yard” is the same length.
Nowadays, scientists define measurements using physical, inalienable processes, rather than physical objects. One example of this is the kilogram, which up until 2019 was defined as the weight of a very specific piece of platinum kept in France. It’s not like the piece of platinum was referred to every time something needed to be weighed, but having a definition for a kilogram was important. And the problem that was found is that the kilogram was losing weight for a completely unknown reason. Scientists decided that it was necessary to shift the definition to rely on universal constants — specifically Planck’s constant — so that the kilogram could never change.
Why The Metric System?
The metric system can be traced back almost entirely to a single person: Gabriel Mouton. Mouton, who was a vicar in Lyon, France, created in 1670 a measurement system that was later called the metric system. The proposals he made — such as basing a unit on the length of a pendulum swing — evolved and changed as scientists and committees continued working on it. The real key to the system was defining measurements in powers of 10, so 10 centimeters is a decimeter, 10 decimeters is a meter, and so on. This makes it a lot easier to do the math on than, say, 12 inches to a foot, three feet to a yard, and 1,760 yards to a mile.
In 1790, the French Academy of Sciences appointed a committee to fully devise a logical system of measurements. The “meter” was defined as a ten-millionth of the distance between the North Pole and the equator, and the “gram” was a cubic centimeter of water. Scientists in France were particularly in favor of this system because the use of powers of 10 made it much simpler than other systems.
After the system was fully devised, it took a few decades to catch on. It wasn’t until 1840 that the metric system was made the official system in France. In 1875, 17 countries (including the United States) attended the Convention of the Metre to further standardize the measurements, and by 1900, 35 countries had adopted the system. Over the past century, the system was steadily adopted by most countries. A universal standard of measurement made it easier for countries to engage in international trade, exchange information and cooperate more generally.
Why Not The Metric System?
With every other country in the world adopting the metric system, you have to wonder why Liberia, Myanmar and the United States are holdouts. There really isn’t a reason, however, and it turns out that both Liberia and Myanmar are already going through the process of “metrication.” This leaves the United States, the lone holdout of the International System of Units.
For a long time, it seemed like the United States would adopt the metric system. The country sent delegates to the Convention of the Metre in 1875, and in 1866 had passed a bill making it lawful to use the metric system in an official capacity. After a century of mixed usage, the United States passed the Metric Conversion Act of 1975, which called for the voluntary conversion to the metric system. What was missing from the act, however, was any sort of deadline. The American push to install the metric system died out, and the United States customary units (slightly different from the Imperial units) stayed in place.
It’s not as though the metric system can’t be found in the United States. No physicist has to convert from meters to yards when working with Americans. And because the country is the outlier, many industries that work internationally have had to adopt the metric system. It’s far from certain whether the United States will ever make the final move to convert everything else to the metric system — changing every mile marker would be an expensive task — but the metric system holds heavy sway in the country.
Places That Mix Systems
If you’ve ever driven around the United Kingdom (on the left side of the road), you might be surprised to see “miles” referred to often in a country that allegedly uses the metric system. As it turns out, there are many countries that haven’t fully committed to metrication. The reason seems to be that making the shift from one to the other is a hard change for a huge group of people to adapt to.
The United Kingdom, which committed to switching to the metric system in 1965, still uses Imperial units in many places, especially on the road. Ireland, too, still uses the Imperial system in places; it’s hard to imagine ever calling a glass of draught beer anything but “a pint,” though. Malaysia has the metric system, but also uses Malay measurements in places, particularly in traditional markets. The Imperial system, too, has some bearing there. Canada has Imperial units in places (partially thanks to its proximity to the United States), and North Korea makes use of its traditional Korean units in certain settings. It’s possible to run into non-metric units in Thailand, China, Indonesia, Taiwan and plenty of other countries.
The International System of Units is king of the measurements, but it hasn’t yet taken over the whole world. While the United States is the most obvious example of a holdout country, there are places all over the world where you’ll find other units of measurement.