Before every nitrox dive, you need to know your maximum operating depth. Exceed it and you risk oxygen toxicity — a seizure underwater with little to no warning.
Use the calculator below to find your MOD instantly. Set your O2 percentage to match your cylinder analysis, choose your PPO2 limit, and you have your number.
MOD stands for Maximum Operating Depth. It's the deepest point at which it is safe to breathe a given nitrox mix without exceeding your chosen partial pressure of oxygen limit.
Breathing oxygen at high partial pressures causes central nervous system oxygen toxicity. Symptoms can include convulsions underwater with little or no prior warning — which is why diving beyond your MOD is one of the more serious mistakes you can make on a nitrox dive.
| PPO2 Limit | Use Case | Notes |
|---|---|---|
| 1.2 bar | Conservative | Recommended for long exposures or rebreather diving |
| 1.4 bar | Working limit | Standard working limit per PADI and most agencies |
| 1.6 bar | Absolute maximum | Contingency limit only — not for planned bottom time |
Divide your PPO2 limit by your fraction of oxygen, subtract 1, then multiply by 33 for feet of seawater or 10 for meters of seawater.
For example: 32% nitrox with a 1.4 PPO2 limit gives (1.4 / 0.32) - 1 = 3.375, then 3.375 x 33 = 111 feet.
| Mix | MOD at 1.4 PPO2 | MOD at 1.6 PPO2 |
|---|---|---|
| EAN28 | 112 ft / 34 m | 132 ft / 40 m |
| EAN32 | 95 ft / 29 m | 112 ft / 34 m |
| EAN36 | 82 ft / 25 m | 95 ft / 29 m |
| EAN40 | 69 ft / 21 m | 79 ft / 24 m |
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