Depending on the purpose, the following definitions of breadth (B) are used:
1. The maximum breadth of the ship, measured amidships to the moulded line of the frame in a ship with a metal shell and to the outer surface of the hull in a ship with a shell of any other material, (MARPOL).
2. The extreme width from outside of the frame to outside of the frame at, or below, the deepest subdivision load line, (SOLAS).
- Extreme breadth – The maximum breadth over the extreme points between port side and starboard of the ship.
- Moulded breadth – The greatest breadth of the ship measured between the inside edges of the shell plating.