Weight Converter
Convert a weight or mass between metric units (tonnes, kilograms, grams, milligrams) and the pound-based units used in the United States and the United Kingdom, including stone and the two kinds of ton. The factors are exact.
Result
Enter a value to convert.
The calculation runs in this browser tab. Nothing you enter is uploaded, saved or logged.
What is the difference between weight and mass, and how are the units defined?
Strictly, mass is the amount of matter in an object and weight is the force of gravity on it. In everyday use, and on kitchen and bathroom scales, “weight” means mass, and kilograms and pounds are both units of mass. This converter works with mass, so a result is the same on the Moon as on Earth.
The kilogram is the SI base unit. Since 2019 it is defined from the Planck constant rather than from a metal cylinder. The pound is defined from it: under the international agreement of 1959, one avoirdupois pound is exactly 0.45359237 kilogram. From the pound follow the ounce (1/16 pound), the stone (14 pounds), the US ton (2,000 pounds) and the UK or long ton (2,240 pounds).
How to use the Weight Converter
- Enter the weight to convert. Negative values are not accepted because a mass cannot be negative.
- Choose the unit you are converting from and the unit you are converting to.
- Read the result, the conversion factor and its inverse. A leading ≈ means the value was rounded to the precision you selected.
- Use the table to see the same weight in every unit, and Copy result to copy the number alone.
Formula
- General rule
- result = value × (kg per source unit) ÷ (kg per target unit)
- Pounds to kilograms
- kg = lb × 0.45359237
- Kilograms to pounds
- lb = kg ÷ 0.45359237 ≈ kg × 2.2046226
- Ounces to grams
- g = oz × 28.349523125
Equivalents among pound-based units are whole numbers: 16 oz = 1 lb; 14 lb = 1 stone; 2,000 lb = 1 US ton; 2,240 lb = 1 UK ton.
The tonne (t) is the metric ton, 1,000 kg. It is close to, but not the same as, the US ton (907.18 kg) or the UK ton (1,016.05 kg).
Worked example
A body weight of 150 pounds in kilograms. These are the results the converter gives:
| Question | Result |
|---|---|
| Input: Value | 150 |
| Input: From | Pounds (lb) |
| Input: To | Kilograms (kg) |
| Input: Precision | 10 significant digits |
| 150 lb equals | 68.0388555 kg |
| Conversion factor | 1 lb = 0.45359237 kg |
| Inverse | 1 kg = ≈ 2.204622622 lb |
| Formula | kg = lb × 0.45359237 |
Assumptions and limits
- The ounce here is the avoirdupois ounce (28.349523125 g). The troy ounce used for gold and silver is heavier, about 31.1035 g, and is not included.
- Carats are metric carats (0.2 g) for gemstones, not the karat that measures the purity of gold.
- The “pound” is the pound-mass; pound-force and other force units are not converted.
- Results are shown to 6 to 15 significant digits; non-terminating conversions such as kilograms to pounds are rounded and marked ≈.
Frequently asked questions
How many pounds are in a kilogram?
One kilogram is about 2.2046226 pounds. Going the other way, one pound is exactly 0.45359237 kilogram.
How do I convert pounds to kilograms?
Multiply the pounds by 0.45359237. For 150 lb that gives 68.0388555 kg. A quick estimate is to halve the pounds and subtract a tenth of that: 150 → 75 − 7.5 = 67.5.
How many ounces are in a pound?
Sixteen. One avoirdupois ounce is therefore 1/16 of a pound, or 28.349523125 grams.
How many pounds are in a stone?
Fourteen. A person who weighs 11 stone 4 pounds weighs 158 pounds, or about 71.7 kilograms. The stone is still used for body weight in the UK and Ireland.
What is the difference between a ton, a long ton and a tonne?
A US (short) ton is 2,000 lb, about 907.18 kg. A UK (long) ton is 2,240 lb, about 1,016.05 kg. A tonne is the metric ton, exactly 1,000 kg.
Is a kilogram a unit of weight or of mass?
Of mass. Weight is a force and is measured in newtons, but in daily life people use “weight” for mass, and the converter follows that usage.