Gross register tonnage (GRT,grt,g.r.t.,gt), orgross registered tonnage, is a ship's total internal volume expressed in "register tons", each of which is equal to 100 cubic feet (2.83 m3). Replaced byGross Tonnage (GT), gross register tonnage uses the total permanently enclosed capacity of the vessel as its basis for volume. Typically this is used for dockage fees, canal transit fees, and similar purposes where it is appropriate to charge based on the size of the entire vessel. Internationally,GRT may be abbreviated asBRT 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.[1][2]
Gross register tonnage is not a measure of the ship's weight or displacement and should not be confused with terms such asdeadweight tonnage ordisplacement.
Gross register tonnage was defined by theMoorsom Commission in 1849.
Gross and net register tonnages were replaced bygross tonnage andnet tonnage, respectively, when theInternational Maritime Organization (IMO) adopted The International Convention on Tonnage Measurement of Ships on 23 June 1969. The new tonnage regulations entered into force for all new ships on 18 July 1982, but existing vessels were given a migration period of 12 years to ensure that ships were given reasonable economic safeguards, since port and other dues are charged according to ship's tonnage.
Since 18 July 1994 the gross and net tonnages,dimensionless indices calculated from the total moulded volume of the ship and its cargo spaces bymathematical 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.
