Metric and US customary weights
Two families of weight units are in daily use. The metric system starts from the kilogram: a gram is a thousandth of it, a milligram a millionth and a metric ton a thousand kilograms. The US customary system, also called avoirdupois, is built on the pound, divided into 16 ounces. Since 1959 the pound has been defined as exactly 0.45359237 kilogram, so every customary weight converts exactly to metric.
How to use this converter
Enter a value in any field and the other units follow instantly. Start from the unit you have, such as ounces on a food package or kilograms on a luggage tag. Below the converter, each common pair has its own page with the formula, an example and a chart you can print.
Stones, short tons and long tons
Some units only make sense in one country. The stone, worth 14 pounds, is how British and Irish people give their body weight. The word ton covers three different units: the US short ton of 2,000 pounds, the British long ton of 2,240 pounds and the metric ton of 1,000 kilograms, also spelled tonne. They differ by up to 12%, so always check which one a document means.
Handy reference points
- 1 kg ≈ 2.2046 lb, and 1 lb = 453.59237 g
- 1 oz = 28.349523125 g, and 100 g ≈ 3.527 oz
- 1 stone = 14 lb ≈ 6.35 kg
- 1 short ton = 2,000 lb ≈ 907.2 kg
- 1 metric ton = 1,000 kg ≈ 2,204.6 lb
Weight versus volume
Ounces, grams and pounds measure weight. Fluid ounces, cups and milliliters measure volume. Going from one to the other requires the density of the ingredient: a cup of water weighs about 237 g, but a cup of flour only about 125 g. Use a volume converter for liquids, and a kitchen scale whenever a recipe is precise.
Weight units compared
| Unit | Symbol | In kilograms |
|---|---|---|
| Microgram | mcg | 1 × 10⁻⁹ |
| Milligram | mg | 0.000001 |
| Gram | g | 0.001 |
| Kilogram | kg | 1 |
| Metric ton | t | 1,000 |
| Ounce | oz | 0.0283495 |
| Pound | lb | 0.453592 |
| Stone | st | 6.35029 |
| Short ton | ton (US) | 907.185 |
| Long ton | ton (UK) | 1,016.05 |
The units in detail
What is a microgram?
The microgram is one millionth of a gram, written µg in science and mcg on US drug and supplement labels to avoid confusion with mg. Vitamin D, vitamin B12 and folate doses are given in micrograms because the amounts are so small.
What is a milligram?
The milligram is one thousandth of a gram. It is the everyday unit of medicine doses (a regular aspirin tablet holds 325 mg), caffeine content and the sodium, cholesterol and mineral lines of a Nutrition Facts label.
What is a gram?
The gram is one thousandth of a kilogram, roughly the mass of a paper clip. It is the unit of kitchen scales and recipes outside the US, of nutrition labels (protein, fat and sugar per serving) and of postage for small parcels.
What is a kilogram?
The kilogram is the SI base unit of mass. Since 2019 it has been defined from the Planck constant rather than from a metal cylinder kept near Paris. Most countries use it for body weight, luggage allowances and groceries; one kilogram is about 2.2 pounds.
What is a metric ton?
The metric ton, or tonne, equals 1,000 kilograms, about 2,204.6 pounds. It is the unit of shipping, vehicle weights outside the US, crop harvests and carbon dioxide emissions. It sits between the US short ton and the British long ton.
What is an ounce?
The avoirdupois ounce is one sixteenth of a pound, exactly 28.349523125 grams. Americans use it for food portions, packaged goods and baby weights. It is a weight, not to be confused with the fluid ounce used for volume, or the troy ounce used for gold.
What is a pound?
The international avoirdupois pound has been exactly 0.45359237 kilogram since 1959, and holds 16 ounces. It is the US unit for body weight, groceries, shipping and gym plates. The abbreviation lb comes from libra, the Roman pound.
What is a stone?
The stone equals 14 pounds, about 6.35 kilograms. It is still how people in the United Kingdom and Ireland state their body weight, as in 11 st 4 lb. It is rarely used in the United States or for anything other than people.
What is a short ton?
The short ton is the US ton: 2,000 pounds, about 907.18 kilograms. Truck payloads, gravel, coal and steel deliveries in the United States are quoted in short tons, usually just called tons.
What is a long ton?
The long ton, or imperial ton, equals 2,240 pounds, about 1,016.05 kilograms. It was the British ton before metrication and is still used for the displacement of ships and some international commodity contracts.