Measurement Ton
Modern equivalent
40 cubic feet = 1.133 cubic metres
A freight ton of 40 cubic feet, used to charge for cargo that is bulky rather than heavy.
A third cubic ton, and a different size again. Where the register ton is a hundred cubic feet, the measurement ton is forty, and it exists to solve a pricing problem: light bulky freight fills a ship long before it weighs her down.
So a carrier charges by whichever is greater, the weight of the consignment or its volume in measurement tons. Feathers and furniture pay by space, pig iron pays by weight, and the shipping line is paid properly for either.
It leaves British shipping with tonnages that are volumes — gross and net, counted in register tons of a hundred cubic feet, and freight charged in measurement tons of forty — and two that are weights, all using the same word.