| Reference | Stones (st) | Long tons (t) |
|---|---|---|
| A sheet of A4 paper (80 gsm) | 0.000787365 st | 0.00000492103 t |
| One litre of water | 0.157473 st | 0.000984207 t |
| Average adult human | 11.0231 st | 0.0688945 t |
| A small car | 220.462 st | 1.37789 t |
The stone is a unit of mass equal to 14 pounds, or about 6.35029 kilograms. Its symbol is st. It is a British unit with an unusual property: it is almost entirely confined to one purpose, human body weight, and almost entirely confined to Britain and Ireland.
Before standardisation the stone was not a fixed quantity at all. It varied by commodity and by region, from eight pounds for meat to twenty-four for certain wools, and a stone of one good was simply not a stone of another. The Weights and Measures Act of 1835 fixed it at fourteen pounds for all purposes, ending a genuine source of commercial dispute.
Its survival is a study in how measurement habits actually change. Britain converted trade to metric units over decades, and shops now weigh in kilograms, but personal weight remained stubbornly in stones and pounds. A person who buys potatoes by the kilogram will still say they weigh eleven stone four. Medical practice sits awkwardly between the two, with charts in kilograms and patients who think in stones, so most clinical software displays both.
The convention is to give a whole number of stones followed by the remaining pounds, never a decimal, so twelve stone six means 174 pounds. This makes mental conversion to metric awkward and is one reason the unit has no traction outside its home. Ireland uses it similarly, and Australia and New Zealand abandoned it in the 1970s.
Sport keeps the unit visible where medicine has quietly dropped it. British boxing reports fighters at, say, twelve stone seven, horse racing states the weight a jockey must carry in stones and pounds, and rowing crews are selected against a stone-based limit. Clinical practice has moved the other way: hospital notes, drug dosing and growth charts are all metric, because a dose calculated per kilogram cannot safely pass through a conversion. The result is that many British patients hear their weight in kilograms from a nurse and repeat it in stones to a friend an hour later, translating in their heads at roughly six and a third kilograms to the stone.
One stone equals 14 pounds, about 6.35029 kilograms, or 224 ounces.
The long ton is a unit of mass equal to 2240 pounds, or about 1016.047 kilograms. It is the ton of the British imperial system, sometimes called the imperial ton or the gross ton, and it sits within one and a half per cent of the metric tonne, which is both convenient and a persistent source of error.
Three tons compete for the same word. The long ton is 2240 pounds, the short or American ton is 2000 pounds, and the tonne is 1000 kilograms, roughly 2204.6 pounds. The long ton and the tonne differ by about sixteen kilograms, small enough to be invisible in a rough estimate and large enough to matter across a shipload. Contracts, customs declarations and commodity quotations therefore name the ton explicitly rather than relying on context.
Its structure follows the rest of the imperial system: twenty hundredweight of 112 pounds each. That is where the 2240 comes from, and it makes the long ton the natural top of a chain running pound, stone, hundredweight, ton, each step a whole number of the last.
British shipping, mining and steel used it for well over a century, and it survives in some maritime contexts and in older engineering literature. The displacement of warships is still often quoted in long tons, which is why published figures for historic vessels can differ by a couple of per cent depending on which ton the source used.
Shipping complicates the word further by using ton for things that are not masses at all. A register ton is a hundred cubic feet of enclosed space, used to size a vessel for harbour dues; a freight ton may be a mass or a volume, whichever yields the larger charge; and displacement, the figure by which warships are described, is the mass of water a hull pushes aside, historically stated in long tons. Reading a ship's particulars therefore means checking which ton is meant before comparing anything. Deadweight tonnage, the cargo, fuel and stores a ship can carry, is a mass and is now given in metric tonnes, but older registers state it in long tons.
One long ton equals 2240 pounds, about 1016.047 kilograms, or 1.12 short tons.