Pounds to Kilograms

Body weight, luggage allowances, shipping charges and gym plates cross this boundary constantly. The factor is exact — a pound is defined as exactly 0.45359237 kilograms — so nothing is lost in the conversion, which is more than can be said for the rules of thumb people use instead.

How it is calculated

kg = lb × 0.45359237

Halving and subtracting a tenth gets close, because 0.45 is near enough for a rough check, but the error reaches almost a kilogram by the time you are weighing a person. The exact factor costs nothing to use.

Source: NIST SP 811 (2008), Appendix B.8 — pound (avoirdupois) (lb) to kilogram (kg) = 4.535 924 E−01

Common values

Questions people ask

What is 150 pounds in kilograms?

68.0388555 kilograms, which is what a scale would read to six decimal places and what everyone rounds to 68. For body weight that rounding is far below the swing of a single day.

Is a pound the same as a pound-force?

No, and the distinction matters outside everyday use. The pound here is a unit of mass. Pound-force is a unit of weight — mass times gravity. On Earth the numbers look alike, which is exactly why they get confused in engineering work where they should not be.

What about stones?

A stone is 14 pounds, so it is 6.35029318 kilograms. Weight in Britain is often given as stones and pounds together, so convert the whole figure to pounds first and only then to kilograms.

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