Gross TonnageGT
A dimensionless measure of a ship’s total internal volume, used for regulation, manning and port-due calculations.
Gross tonnage (GT) is a measure of the total enclosed volume of a ship, calculated by a formula under the International Convention on Tonnage Measurement of Ships. Despite the word "tonnage", it is a volume-based, dimensionless index — not a weight.
GT drives regulatory thresholds (which conventions apply), safe-manning requirements, registration fees and many port and canal dues. Net tonnage (NT), a related figure, estimates the volume available for cargo. Neither should be confused with deadweight, which is a weight.
On The Maritime
Also known as: gross tons, GT, gross registered tonnage.
Related terms
Deadweight TonnageDWT
The total weight a ship can carry — cargo plus fuel, stores, crew and water — at her load line, in metric tonnes.
Net TonnageNT
A volume-based measure of the space available for cargo and passengers, derived from gross tonnage.
Draught
The vertical distance from the waterline to the bottom of the keel — how deep the ship sits in the water.
Plain-English reference definition — our own explanation of a standard shipping concept, not a licensed source or legal advice. See the full glossary or the broader maritime dictionary.
Last reviewed: June 2026.