Most ships I think are recorded using "dwt" which is short for deadweight tons. The deadweight of a ship is the weight of what it carries, which is mostly its cargo, but also includes fuel, stores, etc. The weight of the ship itself is called its "lightweight". Deadweight + lightweight = displacement.
In the shipping world, a ton is not always a measurement of weight. The confusion is caused by the old custom of measuring merchant ships' capacity in 'tons' of 100 cubic feet. (Originally the 'tons' or 'tuns' were large barrels used to carry cargo).
Two tonnages are calculated for merchant ships. Gross Registered Tonnage (GRT) measures the interior volume of the ship, with a few minor exceptions. Much of this volume is unprofitable to the owners, but it is the measurement generally quoted, as it gives a general idea of a ship's size. Net Registered Tonnage is also calculated. This includes only the volume capable of being used for profitable purposes and excludes spaces unavailable to passengers or cargo, such as the engineroom, fuel tanks and the crew's quarters. Taxes and charges are often based on NRT.
The real weight of a merchant ship is generally only of interest to her designers. It is known as displacement, as it is equal to the weight of the water displaced by the ship when floating at her designed waterline. Deadweight varies widely, according to the ship's function. A large cruise ship may have a deadweight of as little as 7,000 tons, while a very large oil tanker may have a deadweight of more than 300,000 tons. It may be noted that that deadweight is generally given in British tons of 2,240 pounds, or in tonnes of 1,000 kilograms.
So using only 'GRT - gross tonnage' as a comparison:
Titanic - 46,238 tons
Knockl Nevis - 236,710 tons
Freedom - 158,000 tons
The confusion arises between what is important to ship designers and builders, the Board