Weight Converter
Convert mass between kilograms, grams, milligrams, pounds, ounces, stone and metric tonnes, with a stone-and-pounds reading.
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Updated Formula covered by automated tests
Enter an amount in kilograms, grams, milligrams, pounds, ounces, stone or metric tonnes and the converter lists the equivalent in every other unit, plus a stone-and-pounds reading for body weight. Typical uses are reading a European recipe that weighs flour in grams, checking a parcel against a courier limit given in pounds, comparing gym plates marked in kilograms with a program written in pounds, or translating a British friend’s weight from stone.
Strictly speaking, all of these units measure mass, the amount of matter in an object, while weight is the force gravity puts on that mass. Bathroom and kitchen scales measure force but are calibrated to display mass, so in daily life the two words are used interchangeably and the converter follows that convention.
The formula
- kg per source unit
- Kilograms in one unit of what you typed, for example 0.45359237 for pounds
- kg per target unit
- Kilograms in one unit of the result, for example 0.001 for grams
- st
- Stone, a British unit of 14 pounds still used for body weight in the UK and Ireland
Every input is turned into kilograms and then divided by the kilogram value of each output unit. The avoirdupois pound used in shops, kitchens and gyms has been defined since 1959 as exactly 0.45359237 kg, so pounds, ounces and stone are all fixed fractions or multiples of the kilogram with no rounding involved.
The kilogram itself was defined by a platinum-iridium cylinder kept near Paris from 1889 until May 2019. Since then it has been fixed through the Planck constant, which lets national laboratories realize it anywhere with an instrument called a Kibble balance. None of this changed everyday values: a kilogram of sugar weighs the same as it did before the redefinition.
Worked example
Tom, who grew up in Manchester, tells a US doctor’s office he weighs 11 stone 4 pounds. The intake form asks for pounds and the clinic’s software wants kilograms.
- 1 Convert the stone to pounds: 11 × 14 = 154 lb.
- 2 Add the extra pounds: 154 + 4 = 158 lb.
- 3 Multiply by the exact pound definition: 158 × 0.45359237 = 71.6676 kg.
- 4 Check by dividing back: 71.6676 ÷ 0.45359237 = 158.0 lb, which splits into 11 st 4 lb.
Result: Tom weighs 158 lb, or 71.7 kg. Rounding the pound to 0.45 kg would have given 71.1 kg, about 0.6 kg too low.
Before you rely on the result
- Only avoirdupois units are included; troy ounces, carats and grains are not.
- Converting cups or spoons to grams depends on the ingredient’s density and needs a cooking converter, not a mass converter.
- Displayed values are rounded to about six significant figures, which is far finer than any household scale can read.
Frequently asked questions
Is a gold or silver ounce the same as a kitchen ounce?
No. Precious metals are priced in troy ounces of 31.1034768 g, about 10 percent heavier than the 28.349523125 g avoirdupois ounce used for food and postage. This converter uses avoirdupois ounces, so do not use it to value bullion.
What is the difference between a tonne, a short ton and a long ton?
The metric tonne shown here is 1,000 kg. The US short ton is 2,000 lb (907.18474 kg) and the British long ton is 2,240 lb (1,016.0469088 kg). Shipping and freight documents usually say which one they mean; if they write "ton" without a qualifier in the US, assume the short ton.
Why does my weight show differently on two scales?
The conversion is exact, so a difference between a kilogram scale and a pound scale comes from the scales themselves: calibration, a soft floor, or rounding to the nearest 0.1 kg versus 0.2 lb. Weigh yourself on one scale at the same time of day if you are tracking a trend.
How do I write 80 kg in stone and pounds?
Divide by 0.45359237 to get 176.37 lb. Divide by 14 to get 12 whole stone (168 lb) and keep the remaining 8.37 lb, which most people round to 12 st 8 lb.
Sources
- NIST: Kilogram, mass and Planck’s constant (nist.gov)
- NIST: Unit conversion (SI and US customary units) (nist.gov)