Metric vs Imperial: Why the World Still Uses Both
Only three countries have not officially adopted the metric system — but almost every metric country still buys pints, inches or acres.
11 May 2026 · 6 min read · Reference
The story that "only America uses imperial" is much too simple.
Where the systems came from
Imperial units grew from body parts and farm practice: a foot, a hand, a pace, an acre (the land a team of oxen could plough in a day). They were standardised by the British Weights and Measures Act of 1824, long after they were already in use.
Metric was designed on purpose in revolutionary France in the 1790s, on a decimal base tied to nature — the metre was originally one ten-millionth of the distance from the equator to the North Pole.
Who uses what
Officially, only the United States, Liberia and Myanmar have not adopted metric as their primary system. But adoption is rarely total:
- UK — metric by law for trade, yet road signs are in miles, beer is sold in pints, and body weight is spoken in stones.
- Canada — metric officially; lumber, plumbing and cooking remain imperial.
- India — fully metric since 1957, but land is still traded in bighas, cents and gunthas.
- Japan — metric, except for rooms measured in tatami mats and rice in gō.
- US — imperial in daily life; science, medicine, the military and the automotive industry are metric.
Why imperial survives
- Sunk infrastructure. Every drill bit, pipe fitting and road sign would need replacing.
- Human scale. A foot is a convenient size for a human body; a metre is not.
- Divisibility. Twelve inches divides by 2, 3, 4 and 6. Ten divides by 2 and 5.
- Culture. People think in the units they grew up with, whatever the law says.
The hidden dependency
Here is the part most people miss: imperial units are legally defined in metric terms. The inch is defined as exactly 25.4 mm, and the pound as exactly 0.45359237 kg. There is no independent imperial standard any more — the yard in the archives is a museum piece. Every imperial measurement is, underneath, a metric one.
That is also why conversions like inches to centimetres are exact rather than approximate.
The practical rule
Use whichever system your audience uses, and state units explicitly on anything that crosses a border. Ambiguity, not the choice of system, is what causes accidents.
Related reading
This article is for general information. Please verify figures against the relevant standard before using them in critical work. About accuracy