Weight Converter – Kilograms, Pounds, Ounces and Stone

Exact weight conversion factors

The international pound is defined as exactly 0.45359237 kilograms. All other imperial weights follow from it: an ounce is 1/16 of a pound (28.349523125 g) and a stone is 14 pounds (6.35029318 kg). Metric units are powers of ten: 1,000 milligrams in a gram, 1,000 grams in a kilogram and 1,000 kilograms in a metric tonne. The converter goes through kilograms, so every pair of units uses the same exact definitions.

Which units are used where?

• Kilograms and grams – food labels, body weight and luggage in most of the world.
• Pounds and ounces – body weight, groceries and postage in the United States; ounces also appear in recipes.
• Stone and pounds – body weight in the United Kingdom and Ireland, for example 11 st 4 lb.
• Tonnes – vehicles, freight and building materials. A metric tonne (1,000 kg) is different from the US short ton (907 kg) and the UK long ton (1,016 kg).

Kilograms to pounds in your head

Multiply kilograms by 2.2 for a quick estimate of pounds: 70 kg is about 154 lb. To go the other way, halve the pounds and subtract 10%: 180 lb is about 81 kg (exactly 81.65 kg). For stone, divide the weight in kilograms by 6.35.

Weight or mass?

Strictly speaking, kilograms and pounds measure mass, while weight is the force gravity exerts on that mass. In everyday language the two are used interchangeably, and scales display mass. To convert to a force in newtons or pound-force, use the force converter.

Ounces versus fluid ounces

An ounce (oz) measures weight and a fluid ounce (fl oz) measures volume. A fluid ounce of water weighs about one ounce, but for flour, sugar or oil the two differ. Use the volume converter or the cooking category of the unit converter for recipes measured in cups and spoons.

Sources

Conversion factors follow the SI definitions in the BIPM SI Brochure and the exact factors for US customary and imperial units in NIST Special Publication 811.