Weight converter
Convert between milligrams, grams, kilograms, tonnes, ounces, pounds and stones. Exact factors, and the troy-versus-avoirdupois trap explained.
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Every weight unit, one page
Pick any two units above. The conversions people look up most often have dedicated pages with reference tables, linked below.
The factors are exact
Since the international yard and pound agreement of 1959, the imperial units have been defined against the kilogram rather than measured against it. Every factor here follows from that definition and nothing is rounded:
| Unit | Kilograms | Note |
|---|---|---|
| Milligram | 0.000001 | |
| Gram | 0.001 | |
| Kilogram | 1 | SI base unit |
| Tonne | 1000 | metric ton |
| Ounce | 0.028349523125 | exact — one sixteenth of a pound |
| Pound | 0.45359237 | exact by definition |
| Stone | 6.35029318 | 14 pounds |
An ounce is not always an ounce
This is the mistake that costs money. There are two ounces in daily use and they differ by about 10%:
| Grams | Used for | |
|---|---|---|
| Avoirdupois ounce | 28.3495 | everything ordinary — food, post, body weight |
| Troy ounce | 31.1035 | precious metals only — gold, silver, platinum |
A “one ounce” gold coin contains 31.1 g, not 28.3 g. This converter uses the avoirdupois ounce, which is the one you want for anything that is not bullion. If a price is quoted per ounce for a metal, assume troy.
A fluid ounce is a third thing again: a measure of volume, not weight, and it lives in the volume converter. A fluid ounce of honey and a fluid ounce of water do not weigh the same.
A ton is three different things
| Name | Kilograms | Where |
|---|---|---|
| Tonne (metric ton) | 1000 | international, and the one in this converter |
| Short ton | 907.185 | United States |
| Long ton | 1016.047 | historical British |
The gap between a short ton and a tonne is over 9%, which is why shipping and freight documents spell out which one they mean. “MT” on a shipping document means metric tonne.
Weight or mass
Strictly, a kilogram is a unit of mass and a pound as used in physics is a unit of force. In every ordinary context — a bathroom scale, a recipe, a parcel — the two are used interchangeably, and that is what this converter does. The distinction only bites in engineering, where the pound-force and the pound-mass are separate units and mixing them silently is a classic source of error.
Where people go wrong
Stones are British, not American. Body weight in the UK and Ireland is usually given
in stones and pounds; in the US it is given in pounds alone. A weight written as 11 4
in a British context is 11 stone 4 pounds, which is 71.7 kg, not 114 of anything.
A metric pound is 500 g, and is not a pound. Several European countries informally call 500 g a Pfund or pond. It is 10% heavier than an imperial pound. The same trap exists in Chinese: a 市斤 is 500 g while a 台斤 is 600 g.