Deadweight tonnage (also known as deadweight abbreviated to DWT, D.W.T., d.w.t., or dwt) is a measure of how much weight

Weight

In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...

 a ship is carrying or can safely carry. It is the sum of the weights of cargo

Cargo

Cargo is goods or produce transported, generally for commercial gain, by ship, aircraft, train, van or truck. In modern times, containers are used in most intermodal long-haul cargo transport.-Marine:...

, fuel, fresh water

Fresh Water

Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...

, ballast water, provisions, passengers, and crew

Crew

A crew is a body or a class of people who work at a common activity, generally in a structured or hierarchical organization. A location in which a crew works is called a crewyard or a workyard...

. The term is often used to specify a ship's maximum permissible deadweight, the DWT when the ship is fully loaded so that its Plimsoll line is at the point of submersion, although it may also denote the actual DWT of a ship not loaded to capacity.

Deadweight tonnage was historically expressed in long ton

Long ton

Long ton is the name for the unit called the "ton" in the avoirdupois or Imperial system of measurements, as used in the United Kingdom and several other Commonwealth countries. It has been mostly replaced by the tonne, and in the United States by the short ton...

s but is now usually given internationally in tonne

Tonne

The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

s. Deadweight tonnage is not a measure of the ship's displacement

Displacement (ship)

A ship's displacement is its weight at any given time, generally expressed in metric tons or long tons. The term is often used to mean the ship's weight when it is loaded to its maximum capacity. A number of synonymous terms exist for this maximum weight, such as loaded displacement, full load...

 and should not be confused with gross tonnage

Gross tonnage

Gross tonnage is a unitless index related to a ship's overall internal volume. Gross tonnage is different from gross register tonnage...

 or net tonnage

Net tonnage

Net tonnage is a dimensionless index calculated from the total moulded volume of the ship's cargo spaces by using a mathematical formula...

(or their more archaic forms gross register tonnage or net register tonnage).