One kilogram is exactly 2.20462262 pounds, because the pound is defined as exactly 0.45359237 kilograms. Everything else is a rounding decision.
The exact formula
Pounds = kilograms × 2.20462262. Going the other way, kilograms = pounds × 0.45359237. Both factors are exact by definition of the international avoirdupois pound, so there is no measurement uncertainty involved — only how many digits you keep.
For weights under a few hundred kilograms, two decimal places in the result is more precision than any bathroom or luggage scale actually delivers.
Mental math that is close enough
Double the kilograms, then add 10% of that doubled number. For 70 kg: double to 140, add 14, giving 154 lb against a true value of 154.32 lb — an error of about 0.2%.
In reverse, halve the pounds and subtract 10%. For 180 lb: half is 90, minus 9 gives 81 kg versus 81.65 kg. Good enough for a conversation, not for a shipping manifest.
Where the rounding actually matters
Airline baggage limits are enforced at the counter with their own scale, so a 23 kg allowance being 50.7 lb rather than 50 lb is a real difference — pack against the kilogram figure when the airline quotes kilograms.
Medication dosing by body weight, freight pricing bands, and competitive weight classes are the other places where a rounded conversion can cross a threshold. Use the exact factor there and round only at the end.
Stone, pounds, and the UK convention
One stone is exactly 14 pounds, or about 6.35 kg. UK body weight is usually stated as stone-and-pounds, so 70 kg is 11 st 0.3 lb rather than 11.02 stone.
Convert to pounds first, divide by 14 for whole stone, and keep the remainder as pounds. That two-step order avoids the common mistake of treating the decimal part of stone as pounds.
Last reviewed 2026-08-31.