Net register tonnage (NRT, nrt, n.r.t.) is a ship's cargo volume capacity expressed in "register tons", one of which equals to a volume of . It is calculated by subtracting non-revenue-earning spaces i.e. spaces not available for carrying cargo, for example engine rooms, fuel tanks and crew quarters, from the ship's gross register tonnage.Units and Systems of Measurement Their Origin, Development, and Present Status
. National Institute of Standards and Technology. Net tonnage is thus used in situations where a vessel's earning capacity is important, rather than its mere size. Net register tonnage is not a measure of the weight of the ship or its cargo, and should not be confused with terms such as

deadweight tonnage Deadweight tonnage (also known as deadweight; abbreviated to DWT, D.W.T., d.w.t., or dwt) or tons deadweight (DWT) is a measure of how much weight a ship can carry. It is the sum of the weights of cargo, fuel, fresh water Fresh water or ...

displacement Displacement may refer to: Physical sciences Mathematics and physics *Displacement (geometry), is the difference between the final and initial position of a point trajectory (for instance, the center of mass of a moving object). The actual path ...

. Gross and net register tonnages were replaced by

gross tonnage Gross tonnage (GT, G.T. or gt) is a nonlinear measure of a ship's overall internal volume. Gross tonnage is different from gross register tonnage. Neither gross tonnage nor gross register tonnage should be confused with measures of mass or weig ...

and

net tonnage Net tonnage (NT, N.T. or nt) is a dimensionless index calculated from the total moulded volume of the ship's cargo spaces by using a mathematical formula. Defined in ''The International Convention on Tonnage Measurement of Ships'' that was adopte ...

, respectively, when the

International Maritime Organization The International Maritime Organization (IMO; ; ) is a List of specialized agencies of the United Nations, specialized agency of the United Nations responsible for regulating maritime transport. The IMO was established following agreement at a ...

(IMO) adopted The International Convention on Tonnage Measurement of Ships on 23 June 1969. The new tonnage regulations entered into force for all new ships on 18 July 1982, but existing vessels were given a migration period of 12 years to ensure that ships were given reasonable economic safeguards, since port and other dues are charged according to ship's tonnage. Since 18 July 1994 the gross and net tonnages,

dimensionless Dimensionless quantities, or quantities of dimension one, are quantities implicitly defined in a manner that prevents their aggregation into units of measurement. ISBN 978-92-822-2272-0. Typically expressed as ratios that align with another sy ...

indices calculated from the total moulded

volume Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...

of the ship and its

cargo In transportation, cargo refers to goods transported by land, water or air, while freight refers to its conveyance. In economics, freight refers to goods transported at a freight rate for commercial gain. The term cargo is also used in cas ...

spaces by

mathematical formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

e, have been the only official measures of the ship's tonnage.International Convention on Tonnage Measurement of Ships
. International Maritime Organization (IMO). However, the gross and net register tonnages are still widely used in describing older ships.

References

{{Ship measurements Nautical terminology Ship measurements

See also

References