ton·nage 
(tŭnĭj)
(tŭnĭj)n.
1. The number of tons of water that a ship displaces when afloat.
2. The capacity of a merchant ship, often measured in units of 100 cubic feet.
3. A duty or charge per ton on cargo, as at a port or canal.
4. The total shipping of a country or port, figured in tons, with reference to carrying capacity.
5. Weight measured in tons.
[TON + -AGE. Sense 3, Middle English, from Old French, from tonne, tun; see TONNE.]