Gross Tonnage (GT)
A dimensionless measure of a ship’s total internal volume, used for regulation, manning and port-due calculations.
- Category
- Vessel Size and Tonnage
- Abbreviation
- GT
- Dictionary entry
- Gross Tonnage
- Last reviewed
How it works
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.
Where it shows up on The Maritime
Also known as: GT, gross tons, gross registered tonnage.
The short dictionary definition is at Dictionary entry: Gross Tonnage. This page is the explainer.
Related terms
Deadweight Tonnage (DWT)
The total weight a ship can carry (cargo plus fuel, stores, crew and water) at her load line, in metric tonnes.
Net Tonnage (NT)
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.
More vessel size and tonnage terms
A 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: .