Short Ton, Long Ton, Tonne: Three Units, One Word "Ton"

Three tons, and none of them equal

"Ton" is used for three genuinely different masses, and a fourth, entirely unrelated usage in shipping covered further down. Every conversion below is exact, because each unit is built from the international pound, fixed at exactly 0.45359237 kg since 1959.

A short ton is about 9.3% lighter than a tonne (907.18474 kg vs 1,000 kg). A long ton is about 12% heavier than a short ton (2,240 lb ÷ 2,000 lb = 1.12 exactly) and about 1.6% heavier than a tonne (1,016.0469088 kg vs 1,000 kg, a difference of 16.05 kg). That 1.6% gap is small enough that "long ton" and "tonne" get substituted for each other in casual commodity and shipping writing, in a way "short ton" never could be, because a 9.3% error is large enough to notice and a 1.6% one usually isn't.

Why long tons survive in shipping and commodities

The long ton is a holdover from British imperial trade, and it persists specifically where British commercial and legal practice set the original convention: international freight contracts, some steel and coal pricing, and ship-tonnage measurement, much of which was standardized under British maritime law while Britain dominated world shipping in the 19th century. Even after the UK itself metricated retail trade, contracts and shipping conventions written under that older framework, and the institutions built around them, kept using the long ton because renegotiating a unit in an existing freight or insurance contract is more disruptive than continuing to use a slightly old-fashioned one.

The deadweight/displacement confusion

Shipping compounds the ton problem with a second layer: "tonnage" in maritime use does not always mean mass at all.

• Displacement tonnage is a real mass: the weight of water a ship displaces, equal to the ship's own total weight, traditionally expressed in long tons.
• Deadweight tonnage (DWT) is also a real mass: the total weight a ship can carry — cargo, fuel, crew, stores, ballast — before it is loaded past its design limit, traditionally in long tons and now increasingly in metric tonnes.
• Gross tonnage (GT), despite the name, is not a mass at all. It is a dimensionless figure derived from a ship's total enclosed volume under the 1969 International Convention on Tonnage Measurement of Ships, descended from the older "register ton" (100 cubic feet, about 2.83 m³, per register ton). A ship's gross tonnage says nothing directly about how much it weighs or how much cargo it can carry.

A "50,000-ton ship" is therefore ambiguous three ways over: it could mean the ship weighs about 50,000 long tons empty (displacement), can carry about 50,000 long tons or tonnes of cargo (deadweight), or has a gross tonnage figure of 50,000 that measures internal volume, not weight, at all. Industry reporting is usually careful to specify which; general reporting often isn't.

Why 2,240 and not a rounder number

The long ton's odd-looking 2,240 lb has a specific origin: it is 20 long hundredweight, and a long (British) hundredweight is 112 lb — 8 stone of 14 lb each, not a round 100. That 112 lb hundredweight is itself inherited from older English avoirdupois trade divisions built around the 14 lb stone, still familiar today as the unit British body weight is quoted in. The US simplified this when it split from British trade convention: the American hundredweight was redefined as a flat 100 lb, discarding the stone-based 112 lb figure entirely, so the American ("short") ton is 20 × 100 lb = 2,000 lb, a genuinely rounder, decimal-friendlier number than its British ancestor. The short ton isn't a rough approximation of the long ton; it's a deliberate simplification of the hundredweight underneath it.

Which one a country defaults to

The US still defaults to the short ton for domestic purposes: coal production statistics, truck weight limits, and casual American usage of "ton" all mean 2,000 lb unless stated otherwise. The UK legally moved to the tonne for commercial and official use during its metrication programme, so British "ton" today, where it appears at all, is mostly a loose colloquialism rather than a defined trade unit. International shipping and commodities sit in between: contracts written or benchmarked against older British-era conventions can still specify long tons explicitly, particularly in bulk freight and some steel and grain pricing, while newer contracts overwhelmingly specify metric tonnes to avoid exactly the ambiguity this guide describes. None of the three units is disappearing on its own; each persists in the specific market that adopted it and never had a strong enough reason to switch.

A worked comparison

Take 10,000 units of "tons" of iron ore, quoted three different ways:

A trading desk that quietly reads "tons" as "tonnes" when the contract actually specifies long tons is off by a shipment-scale 1.6%, small enough to slip past a quick sanity check; the same mistake with short tons is off by 9.3%, large enough that most experienced traders would catch it on the first invoice. The long ton's error survives specifically because it's the more forgivable-looking one.