Three tons, one word
There is no single ton. There are three, they differ by up to 12%, and English gives them all the same name:
- The short ton is 2,000 lb, or 907.185 kg. This is what “ton” means in the United States.
- The long ton is 2,240 lb, or 1,016.047 kg. This is what “ton” historically means in the United Kingdom, and it still appears in shipping and in older British engineering.
- The tonne, or metric ton, is exactly 1,000 kg. It is the one used almost everywhere else, and in international trade generally.
The odd number behind the long ton is not arbitrary: an imperial hundredweight is 112 lb rather than 100, being eight stone, and twenty of those make 2,240. The American hundredweight was rounded to a literal hundred pounds, and twenty of those make 2,000. So the two tons diverge because the two hundredweights diverged first.
A long ton is exactly 1.12 short tons — a clean ratio, which makes the error easy to spot after the fact and easy to miss at the time. On a bulk order of aggregate or steel, reading one as the other is a 12% quantity error in whichever direction hurts. This converter lists all three separately, with their pound counts on the option itself.
Stone, and where it survives
The stone is fourteen pounds, or 6.350 kg, and it is the unit in which people in Britain and Ireland state their own body weight in ordinary conversation. It is essentially unused in the United States, where the same figure would be given in pounds alone, and unused in metric countries, where it would be kilograms.
It is normally written as a compound — 11 st 4 lb rather than 11.29 st — and the same trap applies as with feet and inches: the decimal fraction is not the pounds. 11.5 st is 11 st 7 lb, because half of fourteen is seven, not five. To convert a compound by hand, multiply the stone by fourteen, add the pounds, and convert once.
This is worth knowing beyond conversation, because British medical records, weight loss programmes and gym equipment all use it, and a figure copied from one into a form expecting kilograms without conversion is out by a factor of about six.
Mass or weight?
Strictly, this is a mass converter. Mass is how much matter something contains and does not change with location; weight is the force gravity exerts on that mass, and it does. An object with a mass of 70 kg has the same mass on the Moon and weighs about a sixth as much there.
The page is called a weight converter because that is what people search for and say, and in everyday use the distinction is invisible: bathroom scales are calibrated for Earth’s surface gravity, so a scale reading in kilograms or pounds is reporting a mass. Kilograms, pounds, ounces, stone and all three tons are units of mass, and every conversion on this page is mass-to-mass.
The distinction becomes real the moment a unit of force appears. Pounds-force (lbf), newtons and kilograms-force are forces, not masses, and they do not belong on this page — a pound and a pound-force are numerically equal only under standard gravity, which is a coincidence of definition rather than an identity. If a specification gives a figure in newtons or lbf, it is describing a load, and converting it as if it were a mass is a category error even when the number happens to come out plausible.
The ounce that measures volume
An ounce is 28.35 g of mass. A fluid ounce is a volume — 29.57 mL in the US, 28.41 mL in imperial measure — and the two are entirely different quantities that happen to share a word and, by coincidence, sit near the same number for water.
That coincidence is exactly what makes the confusion durable. Water has a density near 1 g/mL, so a US fluid ounce of water weighs about 29.6 g, close enough to 28.35 that a rough conversion appears to work. It stops working the moment the substance is not water: a fluid ounce of honey weighs about 42 g, and a fluid ounce of flour about 15 g. There is no fixed factor, because there is no conversion — only a density.
This page carries only the mass ounce. The fluid ounce, in both its US and imperial sizes, lives on the volume converter, and moving between the two needs a tool that asks what the substance is.
Doing it in a spreadsheet
Excel and Google Sheets handle mass through CONVERT, and here the unit codes carry the same trap the words do. "lbm" is the pound,"ozm" the ounce, "kg" and "g" the metric ones, "stone" the stone — and "ton" is the SHORT ton while "uk_ton" is the long one and "t" is the tonne. Three codes, three different masses, and the shortest one is the American default.
For a compound stone-and-pounds figure, the split is the same shape as feet and inches: with total pounds in A1, =INT(A1/14) gives the stone and =MOD(A1,14) gives the remaining pounds. Going in, it is =stone*14+pounds before any conversion.
Sources and methodology
Nothing here is fetched and there is no data feed: every figure is computed from what you type. The arithmetic needs no authority; the definitions do, and that is what the sources settle — the pound as an exact number of kilograms, the two tons and the hundredweight behind them, the stone in UK law, and the distinction between mass and weight that the word in the title glosses over.