Weight converter for kilograms, pounds, stones and tons
This weight converter changes a quantity between 13 units: metric ones from microgram to tonne, the US and imperial ounce, pound, stone, short ton and long ton, and the specialist troy ounce, carat and grain used for precious metals, gems and ammunition. Every factor is an exact definition, so a pound always becomes 0.45359237 kg with nothing rounded along the way.
The avoirdupois pound and its family
The everyday pound is the avoirdupois pound, fixed by the 1959 international yard and pound agreement at exactly 0.45359237 kilograms. The rest of the system hangs off it:
| Unit | Definition | Exact value in grams |
|---|---|---|
| Grain (gr) | 1/7000 lb | 0.06479891 |
| Ounce (oz) | 1/16 lb | 28.349523125 |
| Pound (lb) | 0.45359237 kg | 453.59237 |
| Stone (st) | 14 lb | 6350.29318 |
| US short ton | 2000 lb | 907,184.74 |
| Long ton | 2240 lb | 1,016,046.9088 |
In the other direction, 1 kg = 2.204622622 lb. That is where the familiar "2.2 pounds per kilo" comes from, and it is about 0.2% short: 70 kg is 154.3235835 lb, whereas 70 × 2.2 gives 154.
Worked examples
150 lb = 68.0388555 kg
11 st = 69.85322498 kg
1 t = 2204.622622 lb
1 ozt = 31.1034768 g
5 ct = 1 gBritish body weights are often given as stones and pounds, such as 11 st 4 lb. Convert that to pounds first (11 × 14 + 4 = 158 lb) and then to kilograms: 158 lb = 71.66759446 kg.
Three different tons
- Metric ton (tonne, t): 1000 kg, or 2204.622622 lb. Standard in science and international trade.
- US short ton: 2000 lb, which is 907.18474 kg. This is what "ton" means in most US contexts.
- Imperial long ton: 2240 lb, or 1016.0469088 kg. Still found in British usage and in ship displacement figures.
One short ton is 0.8928571429 long tons, exactly 25/28. When a document just says "ton", check the country and industry before you convert.
Troy ounces, carats and grains
Gold, silver and platinum are priced per troy ounce, which is 480 grains or 31.1034768 g. That makes it about 10% heavier than the kitchen ounce (1 ozt = 1.097142857 oz). Oddly, the troy pound of 12 troy ounces is lighter than a normal pound, since 1 lb equals 14.58333333 ozt.
Gemstones use the metric carat of exactly 200 mg, so five carats make one gram. Do not confuse it with karat, which measures the purity of gold rather than weight. The grain, at 64.79891 mg, survives in bullet and arrow weights and on some medicine labels; 7000 grains make one pound.
Mass versus weight
Strictly speaking, kilograms and pounds measure mass, the amount of matter in an object. Weight is the force gravity exerts on that mass, properly measured in newtons or pound-force. A 10 kg bag keeps its mass on the Moon but weighs only about one-sixth as much there.
In everyday language "weight" means mass, and that is what this tool converts. When you really need the force, the force converter works in newtons, kilogram-force and pound-force (1 kgf = 9.80665 N).
Related tools
For recipes and lab quantities, the mass converter starts from grams and ounces. To turn a weight into a volume, such as grams of oil into milliliters, you need the material's density, which the density converter helps you express in the right units.