Gross tonnage

Gross tonnage is a dimensionless measure of the total enclosed volume of a ship, calculated under the International Convention on Tonnage Measurement of Ships, 1969 as K1 multiplied by V, where V is the total volume of all enclosed spaces in cubic metres and K1 is 0.2 plus 0.02 times the base ten logarithm of V. It is not a weight and it is not a cargo capacity.

The full article will cover what counts as an enclosed space and what is excluded, the certificate that records the figure, and the many regulatory thresholds expressed in gross tonnage across SOLAS, MARPOL, STCW and the ISM Code. It will also cover the canal tonnages derived alongside it, including the Panama Canal Universal Measurement System and Suez Canal Net Tonnage, which share the volume variable but use different coefficients and therefore produce different numbers for the same hull.