Calculating MOD, PO₂ and EAD When Diving Nitrox

This calculator shows how depth, gas mix, and oxygen exposure relate when diving with Nitrox. It calculates the maximum operating depth (MOD) for a given FO2 and PO2 limit, and highlights when oxygen exposure exceeds safe levels. For a detailed explanation of how MOD is calculated using Dalton's Triangle and why PO2 limits matter, see the Maximum Operating Depth Deep Dive.

What MOD, PO2, and EAD Mean

Maximum Operating Depth (MOD) is the greatest depth you can safely breathe a given Nitrox mix without exceeding your chosen oxygen partial pressure limit. Going deeper than this increases the risk of oxygen toxicity, which can cause convulsions underwater.

Partial Pressure of Oxygen (PO2) is the amount of oxygen pressure you are actually breathing at depth. Even though your mix percentage does not change, pressure increases as you go deeper, so the effective PO2 rises with depth. Managing this value is critical for safety.

Equivalent Air Depth (EAD) is a way to compare how much nitrogen you are absorbing when diving with Nitrox versus plain air. It represents the depth you would be at if you were breathing air and taking in the same amount of nitrogen. This helps divers estimate narcosis risk and track nitrogen loading more easily.

• Fraction of Oxygen (FO2) - The percentage of oxygen in the gas mixture.
• Partial Pressure of Oxygen (PO2) - The pressure exerted by oxygen in the mixture.