Weight Converter
Convert between kilograms, pounds, stone, ounces and grams, including the stone-and-pounds format used in the UK and Ireland.
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Mass and weight are not the same thing
Strictly, mass is the amount of matter and weight is the force gravity exerts on it. A 70 kilogram person has the same mass on the Moon and about a sixth of the weight. Everyday usage conflates the two, and these conversions are mass conversions, which is what people actually want. The distinction only matters in physics and in engineering calculations involving force.
Stone is not decimal
One stone is 14 pounds, and British and Irish body weight is conventionally given as stone-and-pounds: 11 stone 4, not 11.29 stone. Converting 158 pounds to 11.29 stone is arithmetically correct and reads as wrong to anyone who uses the unit. The remainder must be expressed in pounds.
Ounces come in two kinds
The avoirdupois ounce, at 28.35 grams, is the one used for food and general weight. The troy ounce, at 31.10 grams, is used for precious metals and is about 10 percent heavier. A price quoted per ounce for gold means troy, and confusing the two produces an error large enough to matter commercially.
The tonne, the ton and the ton
A metric tonne is 1000 kilograms. A US short ton is 2000 pounds, about 907 kilograms. A UK long ton is 2240 pounds, about 1016 kilograms. Three different units, all commonly written as ton, differing by up to 12 percent. Shipping and freight documents are where this causes real disputes, so the unit should always be stated explicitly.
Exact definitions
Since 1959 the international pound is defined as exactly 0.45359237 kilograms, so pound-to-kilogram conversion is exact rather than measured. The kilogram itself has been defined by the Planck constant since 2019, replacing the physical prototype cylinder that had been drifting measurably against its own copies.
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Frequently Asked Questions
How many pounds are in a stone?
Fourteen. British and Irish body weight is conventionally written as stone and pounds, so 158 pounds is 11 stone 4, not 11.29 stone, which is arithmetically right and reads as wrong.
What is the difference between a troy ounce and a regular ounce?
A troy ounce is 31.10 grams and is used for precious metals; the avoirdupois ounce used for food is 28.35 grams. The troy ounce is about 10 percent heavier, which matters commercially.
How many kilograms in a ton?
It depends which ton. A metric tonne is 1000 kg, a US short ton about 907 kg, and a UK long ton about 1016 kg. Three units share the name and differ by up to 12 percent.
Is the pound to kilogram conversion exact?
Yes. Since 1959 the international pound has been defined as exactly 0.45359237 kilograms, so the conversion is exact by definition rather than measured.
What is the difference between mass and weight?
Mass is the amount of matter; weight is the force gravity exerts on it. These conversions are mass conversions, which is what everyday usage means. The distinction matters only in physics and force calculations.
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Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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