Why the world has two measurement systems
Three countries still hold out against metric. The history is stranger than you think, and the practical advice is simpler than the debate.
5 min read · Reviewed July 2026
Only three countries haven’t officially adopted the metric system: the United States, Liberia, and Myanmar. Everyone else measures in units built on tens. How the world ended up split — and why the US of all places is the big holdout — is a genuinely odd story.
The metric system came out of the French Revolution, designed from scratch to replace a mess of regional units. France in the 1780s had an estimated quarter-million different local measures. A ‘pound’ in one town wasn’t a ‘pound’ in the next, which made trade slow and cheating easy. The revolutionaries wanted units owned by no king and tied to nature — the meter was originally one ten-millionth of the distance from the North Pole to the equator.
America almost went metric — twice
Thomas Jefferson wanted decimal measurement for the young United States and nearly got it; a French scientist carrying reference standards to America in 1793 was literally blown off course by storms and captured by pirates. The moment passed. Congress made metric legal in 1866 and, in 1975, even passed a Metrication Act — but made conversion voluntary. Voluntary lost.
The honest reason the US never switched isn’t stubbornness. It’s that by the time it mattered, America was the world’s biggest industrial economy with an enormous installed base of inch-based machines, drawings, and habits. Switching costs were real and immediate; the benefits were diffuse and long-term. Democracies are bad at that trade.
The quiet truth: the US is half metric already
American science, medicine, and the military run on metric. Your soda comes in liters, your medication in milligrams, your car engine in liters, and the inch itself has been legally defined as exactly 25.4 millimeters since 1959. The customary system survives mostly in daily life — road signs, recipes, body weight — where the switching pain lands on regular people instead of institutions.
Practical advice
Don’t memorize conversion tables. Learn about five anchor points — a meter is about a yard, a kilogram is about 2.2 pounds, 100 km/h is about 62 mph, room temperature is about 20°C, a liter is about a quart — and let a converter handle everything precise. That’s what the tool on our homepage is for, and it uses the exact legal definitions rather than the rounded folk versions.