Nitrox MOD Calculator

About this calculator

The maximum operating depth (MOD) of a nitrox blend is the deepest a diver can descend on that gas mix without the oxygen partial pressure (ppO₂) climbing past a chosen safety limit. It is calculated as MOD = ((ppO₂ limit ÷ FO₂) − 1) × 10, where FO₂ is the fraction of oxygen in the mix (e.g. 0.32 for EAN32) and depth comes out in meters of seawater using the 10 m-per-atmosphere rule.

Recreational nitrox courses from PADI, NAUI, and TDI teach divers to plan dives to a working ppO₂ limit of 1.4 ATA, with 1.6 ATA reserved as an absolute contingency maximum for the bottom portion of a dive — beyond that, oxygen toxicity risk (CNS oxtox) rises sharply. Because a richer mix like EAN36 lets a diver breathe more oxygen at any given depth than air, its MOD is shallower than air's; divers and dive planners use this calculator before every enriched-air dive to confirm the planned depth stays within the mix's safe limit.