Internationally, GRT may be abbreviated as BRT for the German "Bruttoregistertonne".
Net register tonnage subtracts the volume of spaces not available for carrying cargo, such as engine rooms, fuel tanks and crew quarters, from gross register tonnage.
Gross register tonnage was defined by the Moorsom Commission in 1849.
Since 18 July 1994 the gross and net tonnages, dimensionless indices calculated from the total moulded volume of the ship and its cargo spaces by mathematical formulae, have been the only official measures of the ship's tonnage.
[3] However, the gross and net register tonnages are still widely used in describing older ships.