Weight Converter
Exact conversion factors
The kilogram is the SI unit of mass. The avoirdupois pound used in the US and UK has been defined as exactly 0.45359237 kg since 1959, and the other imperial units derive from it:
| Unit | Definition | In kilograms |
|---|---|---|
| 1 ounce (oz) | 1/16 lb | 0.028349523125 kg (28.35 g) |
| 1 pound (lb) | 16 oz | 0.45359237 kg |
| 1 stone (st) | 14 lb | 6.35029318 kg |
| 1 tonne (t) | 1,000 kg | 1,000 kg |
So 70 kg = 70 ÷ 0.45359237 = 154.32 lb, and 150 lb = 150 × 0.45359237 = 68.04 kg.
Where each unit is used
- Stones are still common in the UK and Ireland for body weight: 11 st = 69.85 kg. People usually say "11 stone 4", meaning 11 st and 4 lb.
- Ounces appear in recipes and on food packaging: 250 g of butter is 8.82 oz, and a 16-oz steak weighs 454 g.
- Tonne vs ton: this converter uses the metric tonne (1,000 kg). The US "short ton" is 907.18 kg and the UK "long ton" is 1,016.05 kg — check which one a document means.
Quick estimates
- kg → lb: double it and add 10% (70 kg → 140 + 14 = 154 lb).
- lb → kg: halve it and subtract 10% (150 lb → 75 − 7.5 = 67.5 kg, exact answer 68.04).
- oz → g: multiply by 28, or by 30 for a rough cooking estimate.
Strictly speaking these are units of mass; a bathroom scale displays mass even though we call it weight in everyday language. Need your BMI after converting? The BMI calculator expects kilograms and metres.
Frequently Asked Questions
How many pounds are in a kilogram?
One kilogram equals about 2.2046 pounds. One pound is exactly 0.45359237 kg.
How do I convert stones and pounds to kilograms?
Convert the stones (× 6.35) and the pounds (× 0.4536) separately and add them. 11 st 4 lb = 69.85 + 1.81 = 71.67 kg.
Is a fluid ounce the same as an ounce?
No. An ounce measures mass; a fluid ounce measures volume. Use the volume converter for fluid ounces.