Only three countries don’t use the metric system as their official system of measurement.
Few things are as ubiquitous as the metric system, also known as the International System of Units. Democratic societies, totalitarian regimes, desert nations, and mountainous countries alike all use the decimal system of measurement first devised in the 18th century — all, that is, except Liberia, Myanmar, and the United States. Instead, these countries use imperial (or customary) measurements, such as the foot, yard, and mile, as well as ounces, pounds, and tons. Even among these three nations, Liberia and Myanmar are in the middle of the metrification process, meaning that one day the U.S. will be the lone holdout.
There was a time when the U.S. was also headed in the metric direction. In 1975, Congress passed the Metric Conversion Act, calling for the country’s voluntary conversion to the metric system — the key word there being “voluntary.” President Jimmy Carter tried to implement the transformation, but the effort fell flat during Ronald Reagan’s subsequent administration. Because of the system’s near-ubiquity, however, today some U.S. groups (especially scientists) and businesses choose to use metric measurements anyway. And while many other countries have moved on from their own traditional measurement units, some still retain vestiges of time past. In England, road signs still show miles, while some Asian countries sometimes still use traditional measurements in unofficial capacities. And although the U.S. is unlikely to ditch its customary units any time soon, the country is more metric than meets the eye — after all, we often buy beverages in liters and run 5Ks, even if our recipes call for cups and spoons and our odometers measure in miles.
Although metric measures may seem like immutable facts, their values can change over time. Take, for example, the kilogram. In 1799, scientists forged a cylinder to represent the weight of a kilogram (it was later reforged in 1889 out of a more durable platinum-iridium alloy). For years, this cylinder — kept at the International Bureau of Weights and Measures in Sèvres, France, and known as “Le Grande K” or Big K — represented the international measurement of a kilogram. But on November 16, 2018, representatives from the General Conference on Weights and Measure in Versailles, France, voted to change that definition. Instead of relying on an obscure cylinder kept under lock and key (and one that degraded slightly over time), a kilogram was to be defined in relation to Planck’s constant, which is a fundamental universal constant that relates a photon’s energy to its frequency. In other words, today’s definition of a kilogram is technically 6.626,070,15 × 10-34 kg m2 s–1. Don’t worry — 1,000 grams is also a correct answer.
