According to the International Convention of Tonnage Measurement of Ships of 1969, this is the measure of total capacity of closed spaces of ship inside the hull and superstructures, expressed in nondimensional units with the accuracy of two decimal places.

Until year 2000, the gross tonnage of ship was expressed as GRT (Gross Registered Tonnage). Gross Registered Tonnage - the volume of space within the hull and closed spaces above the deck, designed for cargo, supplies, fuel, passengers and crew, expressed in registered tons. 1RT /registered ton/ = 100 cubic feet = 2.83 cubic meters.

• International Convention on Tonnage Measurement of Ships
  Place of publication: (Dz. Urz. UE z 1983 r. Nr 56, poz. 247, z późn. zm.)