right|thumb|The more heavily loaded a ship is, the lower it sits in the water. Maximum DWT is the amount of weight a ship can carry without riding dangerously low in the water.
right|thumb|Scale for a 6,000-tonne DWT ship
Deadweight tonnage (also known as deadweight; abbreviated to DWT, D.W.T., d.w.t., or dwt) or tons deadweight (DWT) is a measure of how much weight a ship can carry. It is the sum of the weights of cargo, fuel, fresh water, ballast water, provisions, passengers, and crew. In modern international shipping conventions such as the International Convention for the Safety of Life at Sea and the International Convention for the Prevention of Pollution From Ships, deadweight is explicitly defined as the difference in tonnes between the displacement of a ship in water of a specific gravity of 1.025 (corresponding to average density of sea water of ) at the draft corresponding to the assigned summer freeboard and the light displacement (lightweight) of the ship.