capacity of a ship

Cube - The cargo carrying capacity of a ship, measured in cubic feet.

'Tonnage' is a measure of the size or cargo capacity of a ship.

Thus, Builder's Old Measurement estimates the cargo-carrying capacity of a ship in "tons", a measurement that has nothing to do with weight.

In order to estimate the capacity of a ship in terms of 'tun' for tax purposes, an early formula used in England was:

A side note: The capacity of a ship is often expressed in terms of its "displacement", which is the amount of water the ship displaces.

Builder's Old Measurement (BOM or bm) is the method used in England from approximately 1650 to 1849 for calculating the cargo capacity of a ship.

The principle that Brunel understood was that the carrying capacity of a ship increases as the cube of its dimensions, whilst the water resistance only increases as the square of its dimensions.