Weight conversion glossary
15 terms defined in plain English — with the conversion factor attached wherever one applies, and a link to the calculator that uses it.
- Definition-first
- Formulas included
- Cross-linked
4 terms
Units & definitions
Gram (g)
One-thousandth of a kilogram. There are 1,000,000 grams in a metric ton.
The gram is a submultiple of the SI base unit. Because the metric system is decimal, moving between grams, kilograms and tonnes is just a shift of the decimal point: 1 t = 1,000 kg = 1,000,000 g.
Kilogram (kg)
The SI base unit of mass, defined since 2019 by fixing the numerical value of the Planck constant. All ton definitions are expressed in kilograms.
Every ton on this site is defined as a number of kilograms, which is what makes conversions exact. One kilogram is about 2.2046226 pounds.
Megagram (Mg)
The strict SI name for one million grams — exactly the same quantity as a metric ton (1,000 kg).
'Tonne' is the name used in practice; 'megagram' is the coherent SI form. Both equal 1,000 kg, so they are interchangeable in calculations.
Pound (avoirdupois)
The customary unit of mass in the US and UK, equal to exactly 0.45359237 kilograms since the 1959 international agreement.
Both the US short ton (2,000 lb) and the UK long ton (2,240 lb) are defined as a number of pounds, so this constant is the root of both. One kilogram is about 2.2046226 lb.
5 terms
Ton types
Deadweight tonnage (DWT)
A measure of how much mass a ship can safely carry — cargo, fuel, water and stores — expressed in metric tons.
DWT is a mass in tonnes, not a volume. It differs from gross tonnage, which is a volumetric measure of a ship's enclosed space and is not a weight at all.
Metric ton (tonne)
A unit of mass equal to exactly 1,000 kilograms, symbol t. Also spelled 'tonne'; it is the global-standard ton used in trade and science.
The metric ton is a decimal multiple of the kilogram, so the conversion is exact and never needs a rounded factor: kilograms ÷ 1,000 = metric tons. It is a non-SI unit accepted for use with the SI (its strict SI name is the megagram, Mg). Outside the United States, an unqualified 'ton' should be read as a metric ton. It is heavier than a US short ton (907.18474 kg) and lighter than a UK long ton (1,016.0469 kg).
Quintal
A unit of mass equal to 100 kilograms in the metric system, so 10 quintals make one metric ton.
The metric quintal (100 kg) is widely used in agriculture for crop weights. Historical national quintals varied, so modern usage means the 100 kg metric value.
UK long ton
The historical British imperial ton: 2,240 pounds, equal to 1,016.0469 kilograms.
Also called the 'gross ton' or 'imperial ton'. Defined in the Weights and Measures Act as 2,240 lb, it is the heaviest of the three tons — about 1.6% heavier than a metric ton and about 12% heavier than a US short ton. It survives in some UK shipping and older references but has largely been replaced by the metric ton.
US short ton
The ton used by default in the United States: 2,000 pounds, equal to 907.18474 kilograms exactly.
Because it is defined from the avoirdupois pound (1 lb = 0.45359237 kg), the kilogram constant is exact but not round: 2,000 × 0.45359237 = 907.18474 kg. Also called the 'net ton'. It is about 10% lighter than a metric ton, which is why a price quoted 'per ton' means a different quantity in the US than elsewhere.
3 terms
Conversion
Conversion factor
The number of kilograms in one ton, used to convert: multiply tons by it to get kg, or divide kg by it to get tons.
There are three, one per ton type: 1,000 (metric), 907.18474 (US short) and 1,016.0469088 (UK long). Using the wrong factor is the single most common conversion mistake.
Tonne vs. ton (spelling)
'Tonne' always means the metric ton (1,000 kg). 'Ton' is ambiguous — it can mean the metric, US short or UK long ton depending on context.
International and British English write 'tonne' for the metric unit to avoid confusion with the imperial 'ton'. American English writes 'metric ton'. When a source just says 'ton', check the country and industry before assuming a value.
Verified Gross Mass (VGM)
The total weight of a packed shipping container plus its own tare, which SOLAS rules require to be verified before loading — usually stated in kilograms.
VGM figures are given in kilograms and often converted to tonnes for planning. Getting the ton type right matters on international movements where documents mix US and metric conventions.
3 terms
Standards & accuracy
Avoirdupois system
The customary weight system of the US and UK, based on the 16-ounce pound, from which the short ton and long ton are derived.
Since 1959 the avoirdupois pound is exactly 0.45359237 kg, which fixes both customary tons in terms of the kilogram. The name distinguishes it from the troy system used for precious metals.
SI (International System of Units)
The modern metric system, maintained by the BIPM, in which the kilogram is the base unit of mass.
The SI defines the kilogram and accepts the tonne (metric ton) for use alongside it. Every constant this site uses traces back to SI definitions, which is why the conversions are exact rather than approximate.
Significant figures & rounding
The number of digits kept in a converted result. Metric-ton conversions are exact; short- and long-ton conversions carry a non-terminating decimal that is usually rounded.
907.18474 and 1,016.0469088 are exact constants, but dividing by them gives long decimals, so results are rounded for display. This calculator keeps enough digits to stay accurate and shows the exact constant so you can round to your own precision.
Definitions are the easy part
Knowing what a metric ton means is useful. Knowing what your exact figure is in kilograms, for the ton type you actually have, is the part that decides anything.