How the lbs to kg conversion works
Pounds and kilograms measure the same thing on two different scales, and the bridge between them has been a fixed, defined number since 1959, not something measured freshly each time. One avoirdupois pound is exactly 0.45359237 kilograms. That means converting pounds to kilograms is a single multiplication, and it is exact: there is no measurement error built into the formula, only the rounding you choose when you display the answer.
The formula
Here pounds is the avoirdupois pound, the everyday US unit for body weight, and kilograms is the SI unit used almost everywhere else. Multiply by 0.45359237 to go from pounds to kg; divide by it to go back.
Worked example
150 lb to kg: 150 × 0.45359237 = 68.04 kg (68.0388555 kg exactly, before rounding). In UK stones, that is 10 st 10 lb.
Reverse check: 68.04 kg ÷ 0.45359237 = 150.00 lb, confirming the round trip.
A note on stones, for UK readers
A stone is exactly 14 pounds, and it is still how most people in the UK and Ireland talk about body weight even though groceries and luggage are in kilograms. 150 lb splits into 10 stone (140 lb) with 10 lb left over, written 10 st 10 lb. Every result on this page shows the stones-and-pounds form alongside kilograms, so you don't have to do that division separately.
Chart: lbs to kg from 1 to 300 lb
| Pounds | Kilograms | Stones and pounds |
|---|---|---|
| 1 lb | 0.45 kg | 0 st 1.0 lb |
| 10 lb | 4.54 kg | 0 st 10.0 lb |
| 25 lb | 11.34 kg | 1 st 11.0 lb |
| 50 lb | 22.68 kg | 3 st 8.0 lb |
| 75 lb | 34.02 kg | 5 st 5.0 lb |
| 100 lb | 45.36 kg | 7 st 2.0 lb |
| 125 lb | 56.70 kg | 8 st 13.0 lb |
| 150 lb | 68.04 kg | 10 st 10.0 lb |
| 175 lb | 79.38 kg | 12 st 7.0 lb |
| 200 lb | 90.72 kg | 14 st 4.0 lb |
| 225 lb | 102.06 kg | 16 st 1.0 lb |
| 250 lb | 113.40 kg | 17 st 12.0 lb |
| 275 lb | 124.74 kg | 19 st 9.0 lb |
| 300 lb | 136.08 kg | 21 st 6.0 lb |
Reading kilograms on a scale or a label
Bathroom scales sold in the US almost always show pounds, but medical charts, gym equipment, checked-baggage limits, and most of the world's grocery scales use kilograms, so this conversion comes up constantly whether or not you think in metric. For the reverse direction with a pounds-and-ounces breakdown built in, use the kg to lbs converter. And for one form that handles both directions plus grams and ounces together, see the full weight converter.