Find your maximum operating depth for any enriched air mix. Enter your O2 percentage and PPO2 limit to instantly calculate your MOD in feet or meters.
MOD stands for Maximum Operating Depth. It's the deepest depth at which it is safe to breathe a given nitrox mix without exceeding your chosen partial pressure of oxygen (PPO₂) limit.
Breathing oxygen at high partial pressures causes oxygen toxicity, which can lead to seizures underwater with little or no warning. Knowing your MOD before every nitrox dive is not optional — it's a fundamental safety check.
| PPO₂ Limit | Use Case | Notes |
|---|---|---|
| 1.2 bar | Conservative / long exposures | Recommended for dives over 3 hours or rebreather diving |
| 1.4 bar | Working limit | PADI and most agencies recommend this as the standard working limit |
| 1.6 bar | Absolute maximum | Used as contingency limit only — not for planned bottom time |
The formula for calculating MOD is straightforward. Divide your PPO₂ limit by your fraction of oxygen (FO₂), subtract 1, then multiply by 33 for feet of seawater or 10 for meters of seawater.
For example, with 32% nitrox (FO₂ = 0.32) and a PPO₂ limit of 1.4: (1.4 ÷ 0.32) − 1 = 3.375, then 3.375 × 33 = 111 feet.