Panamax specifications have been in effect since the opening of the canal in 1914. These dimensions give clear parameters for ships destined to traverse the Panama Canal and have influenced the design of cargo ships, naval vessels, and passenger ships. The allowable size is limited by the width and length of the available lock chambers, by the depth of water in the canal, and by the height of the Bridge of the Americas since that bridge's construction, along with the clearance under the Atlantic and Centennial Bridges since their constructions in 20 respectively. These requirements also describe topics like exceptional dry seasonal limits, propulsion, communications, and detailed ship design. The limits and requirements are published by the Panama Canal Authority (ACP) in a publication titled 'Vessel Requirements'. Panamax and New Panamax (or Neopanamax) are terms for the size limits for ships travelling through the Panama Canal. Neopanamax ship passing through the new Agua Clara Locks.

Two Panamax ships seen almost touching the walls of the Miraflores Locks. For the film company, see Benjamin Odell (producer). For the medicine named 'Panamax', see Paracetamol.

This article is about the size criteria for ships travelling through the Panama Canal.

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