Displacement
Modern equivalent
Long tons of 2,240 lb
The weight of water displaced by a hull, and therefore the weight of the ship itself.
Displacement is the most physically honest figure of the set: the weight of water a hull pushes aside, which by Archimedes is exactly the weight of the ship and everything in it.
It is the conventional measure for warships, where carrying capacity is beside the point and what matters is how much vessel there is. Merchant ships are quoted in gross tonnage or deadweight instead, which is why comparing a frigate to a container ship by their stated tonnages compares two entirely different quantities.