Kilograms and Pounds: Reading and Rounding kg ↔ lb

The pound used in the US and UK — the international avoirdupois pound — is defined as exactly 0.45359237 kg (NIST Handbook 44, Appendix C). So 1 kg = 1 ÷ 0.45359237 ≈ 2.20462 lb. The first figure is exact; the second is rounded. For a quick estimate, 2.2 is within about 0.2%.

A kilogram is heavier than a pound, so the same mass is a bigger number in pounds:

• kg → lb: multiply by 2.20462 (70 kg → 154.3 lb).
• lb → kg: multiply by 0.45359237, or divide by 2.20462 (150 lb → 68.0 kg).

If your pound figure came out smaller than the kilogram figure, the direction was reversed. A mental shortcut for kg → lb: double it, then add 10% (70 → 140 → 154).

A pound has 16 ounces, not 10. 154.3 lb is 154 lb 5.2 oz, not 154 lb 3 oz. To convert the decimal part: multiply it by 16.

• 0.25 lb = 4 oz
• 0.5 lb = 8 oz
• 0.75 lb = 12 oz

Some scales and labels show decimal pounds, others pounds and ounces; check which before writing a value down. Body weight is also sometimes given in stones and pounds (1 stone = 14 lb); use the stones to kilograms converter for those.

• Round to the precision of the original reading. A bathroom scale reading of 70 kg supports "154 lb", not "154.324 lb".
• Near a limit, compare in the limit's own unit. If a limit is stated in kg, weigh in kg. If you must convert, do not round in your favour: an illustrative 23 kg limit is 50.71 lb, so a 51 lb item is over it.
• Labels that give both units are usually each rounded separately, so they may not convert exactly into each other.

The limit figures here are illustrations, not any carrier's actual rules; check the current rules of the airline or courier.

• Reading decimal pounds as pounds-and-ounces (154.3 lb ≠ 154 lb 3 oz).
• Using 2 or 2.5 as the factor — errors of about 9% and 13%.
• Rounding twice: converting a rounded value back gives a different number from the original.
• Writing "lbs" in technical work; the symbol is lb for both singular and plural.
• Treating pound-force (lbf) or kilogram-force (kgf) as mass units — they measure force.

• Kilograms to pounds and pounds to kilograms converters for the arithmetic.
• How the pound fits into Imperial and US customary units: Metric vs Imperial guide.

Definitions are listed on the methodology page.