Weight Converter
Convert between kilograms, pounds, ounces, grams and stone.
Kilograms and pounds
A pound is defined as exactly 0.45359237 kilograms. That gives 2.20462 pounds per kilogram, which is close enough to 2.2 for mental arithmetic in most situations.
For body weight, doubling the kilograms and adding ten percent gets you close. Someone who is 70 kg is about 154 lb, and the quick method gives 154 exactly.
The two different ounces
The ounce you see on food packaging and postage is the avoirdupois ounce, at 28.3495 grams. Sixteen of them make a pound.
The troy ounce, at 31.1035 grams, is used only for gold, silver and other precious metals. It is about ten percent heavier. When a gold price is quoted per ounce, it is always the troy ounce, and confusing the two overstates or understates a holding by a tenth.
Stone, and why UK body weights look different
A stone is 14 pounds. British and Irish body weights are usually given as stones and pounds, so 11 stone 4 is 158 pounds or 71.7 kilograms. The unit is rare elsewhere and is not used for anything other than body weight.
Common questions
Weight (Mass) Conversion Reference
The kilogram is the SI base unit of mass. It is defined by fixing the numerical value of the Planck constant, making it the most precisely defined unit in the SI system. The pound is defined as exactly 0.45359237 kilograms, so all pound-kilogram conversions are mathematically exact.
Core relationships
- 1 pound (lb) = 0.45359237 kg (exact)
- 1 kg = 2.20462 lb (to 6 significant figures)
- 1 stone = 14 lb = 6.35029 kg
- 1 ounce (oz) = 28.3495 g
- 1 gram = 0.035274 oz
- 1 tonne (metric) = 1,000 kg = 2,204.62 lb
- 1 US short ton = 2,000 lb = 907.185 kg
- 1 UK long ton = 2,240 lb = 1,016.05 kg
Weight versus mass
Technically, weight is a force (mass × gravity) and mass is the amount of matter in an object. In everyday language, people use the words interchangeably. A kilogram of apples weighs about 9.81 newtons on Earth — but we call it "a kilogram" for convenience. This distinction matters in physics and engineering but not in the daily conversions this calculator is designed for.
Common conversion tasks
- Bodyweight: US scales show pounds; UK scales show stones and pounds; most other countries use kilograms. A person weighing 70 kg weighs 154.3 lb or 11 st 0.3 lb.
- Luggage limits: Airlines typically set baggage allowances in kilograms for international flights and sometimes in pounds for US domestic routes. 23 kg is the standard checked bag limit on many carriers, equal to 50.7 lb.
- Cooking: American recipes often list ingredients in ounces and cups. European recipes use grams. 1 oz of butter is about 28 g.
- Gym and fitness: Barbells and weight plates are sold in both kg and lb. A 45 lb plate is approximately 20.4 kg.
- Postage: Postal services charge by weight, often in grams for small items and kg for larger parcels.
Troy weight (for precious metals)
Gold, silver, and other precious metals use troy weight, not avoirdupois weight. One troy ounce = 31.1035 g, which is heavier than a standard ounce (28.3495 g). If you are converting precious metal prices per ounce, confirm that the source is quoting troy ounces.