Weight Converter
Kilograms, pounds, stone and ounces all describe the same quantity in different traditions, and the UK uses several of them at once. This converter handles them in both directions.
Formula
kilograms = value × factor for the unit
- 1 pound = 0.45359237 kg exactly
- 1 stone = 14 lb = 6.35029 kg
11 st 4 lb: (11 × 14) + 4 = 158 lb, × 0.4536 = 71.7 kg
The Defined Factors
As with length, imperial masses are defined against the metric system rather than measured:
- 1 pound = 0.45359237 kg exactly
- 1 ounce = one sixteenth of a pound = 28.349523125 g
- 1 stone = 14 pounds = 6.35029318 kg
For mental arithmetic, kilograms to pounds is double it and add ten percent: 70 kg becomes 140 + 14 = 154 lb, against a true 154.3 lb.
A Ton Is Three Different Masses
This is the conversion that most often goes wrong in shipping and construction, because the word is identical and the values differ by more than ten percent:
- Metric tonne: 1,000 kg — about 2,204.6 lb
- US short ton: 2,000 lb — about 907.2 kg
- UK long ton: 2,240 lb — about 1,016.0 kg
A quoted "20 tons" can therefore mean anything from 18.1 to 20.3 tonnes. When it matters, ask which ton. This converter uses the metric tonne.
Stone, and Why It Trips People Up
British body weight is quoted in stone and pounds, which is a mixed-radix number in disguise, and the usual error is to treat the parts separately.
11 st 4 lb is not 11.4 stone. It is (11 × 14) + 4 = 158 lb, which is 71.7 kg.
Converting the other way needs the same care: 80 kg is 176.4 lb, which is 12 stone with 8.4 lb left over — 12 st 8 lb, not 12.6 st.
Mass Versus Weight
Strictly, the kilogram measures mass, the amount of matter, while weight is the force gravity exerts on that mass. A 70 kg person has the same mass on the Moon and about a sixth of the weight.
In everyday use the distinction is ignored, and harmlessly so, because everything is weighed in the same gravity. It matters in physics, where force is measured in newtons: 70 kg weighs about 687 N on Earth.
Quick Reference
| Unit | In kilograms | Reverse |
|---|---|---|
| 1 ounce | 0.0283495 | 1 kg = 35.274 oz |
| 1 pound | 0.45359237 | 1 kg = 2.2046 lb |
| 1 stone | 6.35029 | 1 kg = 0.1575 st |
| 1 US short ton | 907.185 | 1 tonne = 1.1023 short tons |
| 1 UK long ton | 1,016.047 | 1 tonne = 0.9842 long tons |
Frequently Asked Questions
- How many pounds are in a kilogram?
- 2.20462 pounds. For mental arithmetic, double the kilograms and add ten percent.
- How do I convert stone and pounds to kilograms?
- Multiply the stone by 14, add the leftover pounds, then multiply the total by 0.4536. So 11 st 4 lb is 158 lb, or 71.7 kg.
- How many kilograms are in a ton?
- It depends which ton. A metric tonne is 1,000 kg, a US short ton about 907 kg, and a UK long ton about 1,016 kg.
- Are mass and weight the same thing?
- Not strictly. Mass is the amount of matter and is measured in kilograms; weight is the force gravity exerts on it and is measured in newtons. On Earth the two track each other, so everyday use treats them as one.