From kilograms to pounds and back
The kilogram is the SI unit of mass and the reference for every other unit in this converter. The avoirdupois pound used in the United States, the United Kingdom, Canada and elsewhere has been tied to it since 1959 at exactly 0.45359237 kg. Everything else follows from that one number: an ounce is 1/16 lb, a stone is 14 lb, a US short ton is 2,000 lb and a long ton is 2,240 lb. The UK’s Weights and Measures Act 1985 writes the same pound, stone and ton into law.
Metric units step by powers of ten: 1,000 mg in a gram, 1,000 g in a kilogram, 1,000 kg in a tonne. The converter turns your value into kilograms, then into the target unit, and prints the combined factor in the working line, for example “1 kg = 2.20462262185 lb”.
Strictly speaking, these are units of mass, the amount of matter in an object. Weight is the force gravity exerts on that mass, which is why a 10 kg box would weigh less on the Moon while its mass stayed 10 kg. On Earth the difference is invisible in daily life, scales are calibrated to read mass, and “weight” in kilograms or pounds is the normal everyday word.
Weight formulas
The factors in the second, third and fourth lines are exact. Going the other way produces an endless decimal (1 kg = 2.2046226218… lb), so dividing by 0.45359237 keeps more precision than multiplying by a rounded 2.2.
| Unit | Symbol | Kilograms | Where it is used |
|---|---|---|---|
| Gram | g | 0.001 | Worldwide, food labels and recipes |
| Ounce | oz | 0.028349523125 | US and UK packaging, recipes |
| Pound | lb | 0.45359237 | US everyday use, UK alongside kg |
| Stone | st | 6.35029318 | Body weight in the UK and Ireland |
| Metric tonne | t | 1,000 | Freight and industry worldwide |
| US short ton | ton | 907.18474 | US freight and vehicle ratings |
| Long ton | long ton | 1,016.0469088 | Older UK use, shipping |
The converter does not include troy ounces. Gold, silver and other precious metals are priced in troy ounces of about 31.1 g, which are heavier than the 28.35 g ounce above, so a bullion price per ounce cannot be converted with this tool.
Worked examples
- Convert the stone to pounds: 11 × 14 = 154 lb, plus 4 lb gives 158 lb.
- Multiply by the exact pound: 158 × 0.45359237 = 71.6675945 kg.
- Round for a body weight: 71.7 kg.
- Divide by the kilogram value of a pound: 23 ÷ 0.45359237 = 50.7063203 lb.
- Two decimals are plenty for luggage: 50.71 lb, just over 50 lb.
- One ounce is 28.349523125 g, so 12 × 28.349523125 = 340.19 g.
- Packaging usually rounds this to 340 g.
- A short ton is 907.18474 kg: 1,000 ÷ 907.18474 = 1.1023113 short tons.
- A long ton is 1,016.0469088 kg: 1,000 ÷ 1,016.0469088 = 0.9842065 long tons.
Kilograms and pounds table
| Kilograms (kg) | Pounds (lb) |
|---|---|
| 1 | 2.20462 |
| 2 | 4.40925 |
| 5 | 11.0231 |
| 10 | 22.0462 |
| 20 | 44.0925 |
| 25 | 55.1156 |
| 50 | 110.231 |
| 60 | 132.277 |
| 70 | 154.324 |
| 80 | 176.37 |
| 90 | 198.416 |
| 100 | 220.462 |
| Pounds (lb) | Kilograms (kg) | Stone (st) |
|---|---|---|
| 1 | 0.453592 | 0.0714286 |
| 5 | 2.26796 | 0.357143 |
| 10 | 4.53592 | 0.714286 |
| 50 | 22.6796 | 3.57143 |
| 100 | 45.3592 | 7.14286 |
| 150 | 68.0389 | 10.7143 |
| 200 | 90.7185 | 14.2857 |
| 250 | 113.398 | 17.8571 |
Where weight conversions go wrong
- Reading 11.4 stone as 11 st 4 lb. A stone has 14 pounds, so 11 st 4 lb is 11.29 st. Typing 11.4 into the Value field gives 72.4 kg instead of 71.7 kg.
- Using 2.2 for every conversion. It is close enough in a shop, but for 100 kg the rounded factor gives 220 lb against the true 220.46 lb, and the gap grows with the number.
- Writing “ton” without saying which. A US ton (2,000 lb), a long ton (2,240 lb) and a metric tonne (1,000 kg, about 2,204.6 lb) differ by up to 12%. Shipping and cargo documents should name the unit.
- Confusing ounces of weight with fluid ounces. An ounce on this page is a mass; a fluid ounce is a volume. They only line up for water and liquids of similar density, and the US and imperial fluid ounces differ from each other as well.
Kitchen and bathroom scales are typically readable to a few grams or a tenth of a kilogram. The converter shows up to ten significant digits; round the answer to match the scale you weighed with.
Questions people ask
How many pounds are in a kilogram?
2.20462262 pounds, to nine significant digits. For quick estimates, double the kilograms and add a tenth: 50 kg doubled is 100, plus 10 makes about 110 lb (exact: 110.23 lb).
Is a tonne the same as a ton?
No. A tonne is 1,000 kg. The US ton is about 907 kg and the long ton about 1,016 kg, so the metric tonne sits between them.
Why does the UK still use stone?
Stone remains common for body weight in the UK and Ireland by custom, even though most trade is metric. The converter accepts decimal stone, so convert pounds into a fraction of a stone first.
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, Appendix B, National Institute of Standards and Technology.
- Weights and Measures Act 1985, Schedule 1 (definitions of units), legislation.gov.uk (The National Archives).
- SI Units - Mass, National Institute of Standards and Technology.