A ship's displacement or displacement tonnage, a term usually applied only to naval vessels, is the weight of the water that a ship displaceswhen it is floating. The term is defined ordinarily such that the ship's fuel tanks are full and all stores are aboard. Displacement is the actual weight of the ship, since a floating body displaces its own weight in water (Archimedes' principle).[1][2] Another way of thinking about displacement is the weight of the water that would spill out of a completely filled container were the ship placed into it.