Tonnage can be used to describe various aspects of the carrying capacity of a vessel. The methodology of tonnage calculation is a prescribed process, as per loadline conventions, based off Simpsons rules and adjusted for variance from a standard vessel.
Gross tonnage refers to the total volume of enclosed spaces within a vessel.
Net Tonnage refers to the Cargo carrying capacity of a vessel.
Deadweight tonnage refers to the total weight of the vessel itself with no cargo or consumables on board.