Net Tonnage
Net Tonnage (NT) is a dimensionless measure of the useful, cargo-carrying volume of a ship, calculated under the International Convention on Tonnage Measurement of Ships, 1969. It is derived from the gross tonnage by deducting spaces that cannot carry cargo — machinery, crew accommodation, navigation and similar spaces.
Net tonnage represents the earning capacity of the ship in volume terms, so it is widely used as the basis for charges: port dues, light dues, pilotage, canal tolls and many registration fees are assessed on net tonnage, or a related figure such as the Suez or Panama Canal net tonnage.
Net tonnage is the number that quietly drives a large share of the variable trading costs of a ship. Two ships of the same size can pay very different port and canal charges depending on how their spaces are arranged and measured, so tonnage optimisation at the design stage has a real, lifelong cost impact.
What is the difference between gross and net tonnage?
Gross tonnage measures the total enclosed volume of the ship; net tonnage deducts the non-cargo spaces to represent the useful, earning volume. Net tonnage is always smaller.