What Is Gross Tonnage? Definition, Meaning and Concept

Gross tonnage is a measure of the internal volume of a ship for the purpose of determining what regulations apply, calculating port fees, etc. Although this term sounds like a reference to weight, because it uses the term "ton", it is important to note that it is a measure of volume and does not provide information about the weight of a ship, loaded or empty. This is one of a group of terms used to describe ship characteristics for regulatory purposes.

Each "ton" in this unit of measurement consists of 100 cubic feet (2.83 cubic meters) of space. There are several ways to calculate gross tonnage, looking at ways different cargoes could fit on a ship. Bales and shipping containers will need to stack and take up space differently than something like a warehouse full of grain, where grain can fill every corner of the warehouse. In gross tonnage disclosures, a discussion of the calculation approach used informs readers so they can understand the data they are examining.

Gross tonnage does not include structures above decks and also excludes spaces reserved for crew, passengers, ballast and equipment. It specifically focuses on cargo holds. The higher the gross tonnage, the more the ship can carry. The boat will also have a separate weight rating indicating the maximum weight it can safely carry, as well as the empty weight. Other useful measurements include things like displacement.

This measure may affect the ports a ship can enter, how much it pays to dock, and what types of registration fees are due. These rates are adjusted for size to ensure ships pay a reasonable share based on how much they carry. Staffing requirements and other legal stipulations are also based on gross tonnage. Ships must disclose their measurements so that authorities can ensure that owners and captains operate their vessels responsibly and comply with applicable laws.

Gross tonnage measurements can be determined during the design and engineering phase. Designers want to ensure that a ship meets a stated need and may vary the design to fit the tonnage. Customers may have particular requests depending on what they are carrying and where they are traveling. Knowing the basic characteristics of the boat in advance can be important to obtain loans, insurance and other necessary support before taking delivery of a new boat.