Main objective of tonnage convention is to establish uniform principles and rules with respect to the determination of tonnage of ships engaged on international voyages

The convention came into force on 18 July 1982, so vessels built before this date are considered Existing ships, and those built after this date are considered New ships

The Convention applies to the following ships engaged on
international voyages:

1. New ships;
2. Existing ships which undergo alterations or modifications which the
   Administration deems to be a substantial variation in their existing gross tonnage;
3. Existing ships if the owner so requests
4. All existing ships, twelve years after the date on which the Convention comes into force, except that such ships, apart from those mentioned in (2) and (3) of this paragraph, shall retain their then existing tonnages for the purpose of the application to them of relevant requirements under other existing International Conventions.
   (3) Existing ships to which the present Convention has been applied in accordance with sub-paragraph (2) of this article shall not subsequently have their tonnages determined in accordance with the requirements which the Administration applied to ships on international voyages prior to the coming into force of the present Convention

1. Ships of war; and
2. Ships of less than 24 metres in length.
3. The Great Lakes of North America and the River St. Lawrence as far east as a rhumb line drawn from Cap des Rosiers to VSfest Point, Anticosti Island, and, on the north side of Anticosti Island, the meridian of longitude 63 W;
4. The Caspian Sea; or
5. The Plate, Parana and Uruguay Rivers as far east as a rhumb line drawn between Punta Rasa (Cabo San Antonio), Argentina, and Punta del Este, Uruguay.

The convention entitles the flag states to determine the Gross tonnages and Net tonnages for ships flying their flag either directly or by a recognized organization duly approved to do so

Also it entitles flag states to issue International Tonnage Certificates either directly or by a recognized organization duly approved to do so