Value to convert
Metric and imperial in one place
Type one number and every unit updates at once, so you never chain two conversions and lose precision on the way. A pound is exactly 0.45359237 kg and an ounce exactly 1/16 of that — those are defined values, not measurements, so the conversion is exact.
Where stone still shows up
Body weight in the UK and Ireland is usually given in stone and pounds — 11 st 4 lb rather than 71.7 kg. One stone is 14 pounds, about 6.35 kg. Outside those two countries you will rarely meet it.
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Frequently asked questions
Q. Is a pound exactly 0.45359237 kg?
Yes. The international avoirdupois pound was defined as exactly that in 1959, so pound–kilogram conversions carry no rounding of their own.
Q. Is a metric ton the same as a US ton?
No. The tonne here is 1,000 kg. A US short ton is 2,000 lb (about 907 kg) and a UK long ton is 2,240 lb (about 1,016 kg).
Q. Why does the result sometimes show many digits?
Values are kept to eight significant figures. Very large or very small numbers switch to scientific notation so the digits that matter stay readable.