The Meaning of Deadweight Tonnage of a Ship

Above View Of Cargo Ship at sea

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Deadweight tonnage (DWT) refers to the carrying capacity of a vessel. Deadweight tonnage can be figured by taking the weight of a vessel which is not loaded with cargo and subtracting that figure from the weight of the vessel loaded to point where it is immersed to the maximum safe depth. This depth is noted with a marking on the ship's hull, the Plimsoll line. The safe depth varies by the time of year and water density and, in the case of DWT, the summer freeboard line is the measurement used. The displacement of water due to the load is measured in metric tons (tonnes or 1,000 kilograms).

The deadweight tonnage includes not only cargo, but also the weight of fuel, ballast, passengers and crew, and all of the provisions. It only excludes the weight of the ship itself.


A vessel that weighs 2000 tons unloaded carries 500 tons crew and supplies. It can take on 500 tons of cargo in port, at which time it floats at the summer line of its Plimsoll line. The deadweight of this vessel would, therefore, be 1000 tons.

Deadweight Tonnage vs. Displacement Tonnage

Deadweight tonnage is distinct from displacement tonnage, which includes the weight of the ship as well as its carrying capacity. Lightweight tonnage is the weight of the ship itself, including the hull, decking, and machinery, but not including ballast or any supplies that could be consumed, such as fuel and water (except for the liquids in the engine room systems). Deadweight tonnage is the displacement tonnage minus the lightweight tonnage.