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Gas Management

Nitrox Calculator: MOD & Best Mix

Calculate where a Nitrox mix reaches the selected PPO2 threshold, or find the best mix for a planned depth. The result does not determine whether the gas or dive is safe overall.

Technical Diving
Extend the calculator range to 200m, raise the maximum PPO2 to 2.0 ATA, and show technical gas presets
%

Allowed range: 21 to 100 %.

Oxygen mix presets
ATA

Allowed range: 1 to 1.6 ATA.

Maximum PPO2 presets
m

Allowed range: 1 to 40 m.

PPO2 threshold only

This result finds the depth where the entered mix reaches the selected PPO2 threshold. It does not assess cumulative oxygen exposure, gas density, narcosis, decompression, equipment, or training limits, and is not permission to use the gas or depth.
Best mix for a planned depth

The richest whole-percentage mix that stays at or below the 1.4 ATA PPO₂ selected above at your planned maximum depth. Oxygen is rounded down.

m

Allowed range: 6 to 60 m.

EAN35MOD 30.0 m at 1.4 ATA

For nitrogen loading at depth, open this mix in the equivalent air depth calculator.

About MOD

Maximum Operating Depth (MOD) is the calculated depth where a gas mix reaches a selected partial-pressure-of-oxygen threshold. By itself, it is not a safe-depth determination.

MOD=(PPO2FO2−1)CD\text{MOD} = \left(\frac{\text{PPO}_2}{\text{FO}_2} - 1\right) C_D

Where

PPO2\text{PPO}_2
selected partial pressure of oxygen (ATA)
FO2\text{FO}_2
oxygen fraction, not percentage (0.32 for EAN32)
CDC_D
10 m of seawater per atmosphere

The calculator rounds the result down so it never overstates the limit.

Common PPO2 Planning References

PPO2 > 1.6 ATA

Outside common scuba planning ranges

PPO2 1.4-1.6 ATA

Often reserved for decompression exposure under applicable training

PPO2 ≤ 1.4 ATA

Common recreational working threshold; not an all-hazards check

Result

28.1 m MOD

Frequently Asked Questions

What is Maximum Operating Depth (MOD)?
Maximum Operating Depth (MOD) is the calculated depth where a specific breathing gas reaches a selected partial-pressure-of-oxygen (PPO2) threshold. It does not determine whether the gas or dive is safe overall. Exceeding the calculated MOD also exceeds that selected PPO2 threshold and raises oxygen-toxicity risk.
What PPO2 limit should I use for recreational diving?
A PPO2 of 1.4 ATA is a commonly used recreational working threshold, while some plans use 1.2 ATA for more margin. Values up to 1.6 ATA may be used for limited decompression exposure under applicable technical training. Follow your current training, conditions, and whole-profile oxygen-exposure plan.
What is the MOD for EAN32 (Nitrox 32%)?
With a PPO2 limit of 1.4 ATA, the Maximum Operating Depth for EAN32 (32% oxygen) is 33.75 meters (111.3 feet), which the calculator rounds down to 33.7 m. With a more conservative PPO2 of 1.2 ATA, the MOD drops to 27.5 meters (90.7 feet).
How do I find the best Nitrox mix for a depth?
Divide the PPO2 limit by the absolute pressure at your planned maximum depth and round the oxygen percentage down. At 30 meters (4 ATA) and 1.4 ATA, 1.4 ÷ 4 = 0.35, so the best mix is EAN35. Enter the planned depth in the calculator's best-mix section to apply this to any depth and PPO2.
Why is Nitrox popular among recreational divers?
Nitrox (enriched air) is popular because it contains a higher percentage of oxygen than regular air (21%), which reduces the nitrogen absorbed during a dive. This allows for longer no-decompression limits, shorter surface intervals, and reduced risk of decompression sickness. However, it also means a shallower MOD due to oxygen toxicity limits.
What is oxygen toxicity and why does it matter?
Oxygen toxicity occurs when a diver breathes oxygen at high partial pressures for extended periods. Central Nervous System (CNS) oxygen toxicity is the primary concern for divers, as it can cause convulsions, visual disturbances, nausea, and muscle twitching. A convulsion underwater is life-threatening, which is why staying within MOD limits is critical.

Related Guides

Nitrox & oxygen

Understanding MOD: Maximum Operating Depth Explained

Nitrox & oxygen

Best Nitrox Mix for Any Depth

Nitrox & oxygen

Diving Safety: Essential PPO2 Limits Every Diver Should Know

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