Gross tonnage
Gross Tonnage is a measure of the ships total interior volume and is calculated by multiplying the interior volume “V” of the ship in cubic meters by a variable known as “K” (which varies depending on the ships overall volume).
Gross Tonnage is not to be confused with Gross Registered Tonnage which is explained below.

Net tonnage
Net Tonnage is a measure of the total interior volume of a ship’s cargo spaces and is calculated in much the same way. The total volume of designated cargo spaces in cubic meters is then multiplied by varied number of factors resulting in an official net tonnage value.