Weight & Mass Converter

How this is calculated

Everything is converted to kilograms first and then out again, so there is one conversion step in and one out rather than a table of every possible pair. THE IMPERIAL FACTORS HERE ARE EXACT, NOT APPROXIMATIONS. Since the international yard and pound agreement of 1959, the avoirdupois pound has been defined as exactly 0.45359237 kilograms. Everything else in the imperial column follows from that by definition: the ounce is exactly one sixteenth of it, the stone exactly fourteen pounds, the US short ton exactly two thousand. These are definitions rather than measurements, so the conversion adds no error of its own - any imprecision in the answer arrived with your own figure. ⚠️ THE OUNCE ON THIS PAGE IS THE AVOIRDUPOIS OUNCE, THE ORDINARY ONE. A TROY ounce, used for gold, silver and other precious metals, is a different unit entirely at 31.1034768 grams against the avoirdupois 28.349523125 - about 9.7% heavier. Reading a precious-metal price as if it were quoted in ordinary ounces overstates the quantity by roughly a tenth. Troy is deliberately not offered here for the same reason nautical miles are left out of the length converter: mixing two units that share a name into one dropdown is a reliable way to produce a confident wrong answer. ⚠️ A TON IS THREE DIFFERENT WEIGHTS. The US short ton is 2000 lb (907.18474 kg), the UK long ton is 2240 lb (1016.0469088 kg), and the metric tonne is 1000 kg exactly. The short ton is about 9% lighter than a tonne and the long ton about 1.6% heavier. This tool offers the short ton and the metric tonne; where a source just says "ton", find out which one it means before doing anything with the number. WEIGHT AND MASS ARE NOT THE SAME THING, strictly speaking - mass is how much matter there is, weight is the force gravity applies to it. Everything here converts MASS, which is what kitchen scales, bathroom scales, shipping labels and recipes all actually mean when they say weight. The distinction only starts to matter off the surface of the earth. Results are shown to three decimal places, which is enough to render the exact conversions honestly - a pound really is 16 ounces and 7000 grains - without filling the screen with digits nobody needs. Very large or very small results will show the rounding at that width. This converter handles WEIGHT only. It deliberately does not offer length or volume in the same dropdown, because a single list of mixed units lets you ask for kilograms in litres and get a confident number back for a question that has no answer.

Common questions

Why is there no 'convert to' dropdown?

Because showing every unit at once costs nothing and is more useful. You often want two of them - the metric figure for a form and the imperial one to picture it - and with a second dropdown you would have to run the conversion twice. It also lets you see the relationships directly: a pound lined up against 16 ounces and 453.592 grams is more informative than either number on its own.

Are these conversions exact?

Yes. Since the international yard and pound agreement of 1959 the avoirdupois pound is defined as exactly 0.45359237 kilograms, and every other imperial unit here follows from it by definition - the ounce is exactly a sixteenth of a pound, the stone exactly fourteen pounds, the short ton exactly two thousand. These are definitions rather than measured approximations, so the conversion introduces no error. Any imprecision in the answer came in with your own figure.

Is a troy ounce the same as an ounce?

No, and this is the most expensive mistake on this page. A troy ounce is 31.1034768 grams; the ordinary avoirdupois ounce shown here is 28.349523125 grams. Troy is about 9.7% heavier, and it is the unit gold, silver and platinum are priced in. Reading a precious-metal quote as if it were in ordinary ounces overstates how much metal you are getting by roughly a tenth. Troy is deliberately not offered in the dropdown, because two different units sharing the word 'ounce' in one list is exactly how that error happens.

Which ton does this use?

The US short ton, 2000 pounds or 907.18474 kg. There are two others in common use: the UK long ton at 2240 pounds (1016.0469088 kg) and the metric tonne at exactly 1000 kg. The short ton is about 9% lighter than a tonne, the long ton about 1.6% heavier, and the long ton is about 12% heavier than the short one. If a source just says 'ton', find out which it means before relying on the number - shipping, freight and older engineering documents do not agree with each other.

Why only weight?

Because a single dropdown mixing weight, length and volume lets you ask for kilograms expressed in litres, and a calculator that answers that confidently is worse than one that will not offer it. Keeping one dimension per tool means every conversion on the page is a real one. Length and volume have their own converters.

Is this weight or mass?

Mass, which is what you actually want. Strictly, mass is how much matter something contains and weight is the force gravity applies to it - a kilogram of flour has the same mass on the moon and about a sixth of the weight. In everyday use kitchen scales, bathroom scales, recipes and shipping labels all mean mass, and every unit here converts mass to mass. The distinction only starts to bite in physics problems and off the surface of the earth.

Take it further with AI

Copy this into ChatGPT or Claude with your own numbers filled in. It hands over the figures this calculator worked out, so the answer is built on real arithmetic instead of a guess.

I used the Weight & Mass Converter at https://www.bfcbrilliance.com/tools/weight-converter.

What I entered:
- Weight: ___
- Measured in: ___

What it calculated:
- Kilograms: ___
- Grams: ___
- Milligrams: ___
- Metric tonnes: ___
- Pounds: ___

Use those figures as given — they are already worked out, so please don't recalculate or estimate your own. Help me turn them into a plan: what to buy or do, in what order, roughly what it should cost, and the mistakes people most often make with this job.

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