Section 2(f) in The Merchant Shipping (Tonnage Measurement Of Ships) Rules, 1960
(f)"gross tonnage" means the sum total of the cubic capacity of spaces below the upper deck and spaces permanently covered and closed-in spaces on or above the upper deck (other than such spaces which are exempt from measurement under these rules) and consists of-----(i)the tonnage below the tonnage deck;(ii)the tonnage of the spaces between the tonnage deck and the uppermost complete deck;(iii)the covered and closed-in spaces on or above the uppermost complete deck;(iv)the engine and light and air spaces above the upper deck; and(v)the excess of hatchways;
