Net register tonnage (NRT, nrt, n.r.t.) is a ship's cargo volume capacity expressed in "register tons", one of which equals to a volume of 100 cubic feet (2.83 m3). It is calculated by subtracting non-revenue-earning spaces i.e. spaces not available for carrying cargo, for example engine rooms, fuel tanks and crew quarters, from the ship's gross register tonnage.[1][2] Net tonnage is thus used in situations where a vessel's earning capacity is important, rather than its mere size.