Ships classified as Panamax are of the maximum dimensions that will fit through the locks of the Panama Canal. This size is determined by the dimensions of the lock chambers, and the depth of the water in the canal. Panamax is a significant factor in the design of cargo ships, with many ships being built to exactly the maximum allowable size.
Panamax is determined principally by the dimensions of the canal's lock chambers, each of which is 33.53 metres (110 ft) wide by 320.0 metres (1050 ft) long, and 25.9 metres (85 ft) deep. The usable length of each lock chamber is 304.8 metres (1000 ft). The available water depth in the lock chambers varies, but the least depth is at the south sill of the Pedro Miguel Locks, and is 12.55 metres (41.2 ft) at a Miraflores Lake level of 16.61 metres (54 feet 6 in). The height of the Bridge of the Americas at Balboa is the limiting factor on a vessel's overall height.
A Panamax cargo ship would typically have a displacement of around 65,000 tons.