The displacement or displacement tonnage of a ship is its
Ship displacement varies by a vessel's degree of load, from its empty weight as designed (known as "Lightweight tonnage") to its maximum load. Numerous specific terms are used to describe varying levels of load and trim, detailed below.
The process of determining a vessel's displacement begins with measuring its
The draft observed at each set of marks is averaged to find a mean draft. The ship's hydrostatic tables show the corresponding volume displaced. To calculate the weight of the displaced water, it is necessary to know its density. Seawater (1025 kg/m3) is more dense than fresh water (1000 kg/m3); so a ship will ride higher in salt water than in fresh. The density of water also varies with temperature.