Nitrox Calculator

Find how deep you can go on your nitrox, which mix suits your planned depth, and how much nitrogen you really absorb.

Results update as you type.

Quick examples

Load a full example, then change any value.

Oxygen in your tank (% O₂)

Written on your tank's analysis label. Air is 21%.

Quick picks

ppO₂ limit (bar)

Use 1.4 bar for the dive itself. 1.6 bar is only for deco stops.

Maximum operating depth (MOD)

Within limits

On EAN32, your maximum depth is 33.7 m at a ppO₂ of 1.4 bar. Don't go deeper.

Was this calculator useful?

These tools are educational planning aids; they are not a substitute for dive training, current printed tables or a dive computer. Verify results against your training and always plan within the limits of your certification. Nitrox use requires separate training and certification; analyze the oxygen fraction of every tank before use and mark the MOD on the tank.

About MOD, best mix and EAD

Nitrox has more oxygen than air, so it reaches a dangerous oxygen partial pressure at a shallower depth. MOD (maximum operating depth) is that depth for your mix and ppO₂ limit. Best mix works the other way round and finds the richest mix for a depth you have already picked.

EAD (equivalent air depth) is the depth on air with the same nitrogen partial pressure as your nitrox dive. It shows how much nitrogen you really take up, and it lets you plan the dive with air tables.

With your numbers

Enter valid values to see the calculation worked through with your numbers.

Formula

Maximum operating depth (MOD)

MOD = ((ppO2) ÷ (FO2) − 1) × 10

Best mix

FO2 = (ppO2) ÷ (P)

Equivalent air depth (EAD)

EAD = (((1 − FO2) × P) ÷ (0.79) − 1) × 10

ppO₂ at depth

ppO2 = FO2 × P

Absolute pressure

P = (d) ÷ (10) + 1

Where

FO2: oxygen fraction of the mix (32% = 0.32)
ppO2: oxygen partial pressure, or the limit you picked (bar)
P: absolute pressure at depth (bar)
d: depth (m)
0.79: nitrogen fraction of air

How it's calculated

Absolute pressure (bar) = depth ÷ 10 + 1.
MOD (m) = (ppO₂ limit ÷ FO₂ − 1) × 10, rounded down to 0.1 m.
Best mix FO₂ = ppO₂ limit ÷ absolute pressure, rounded down to the whole percent.
EAD (m) = ((1 − FO₂) ÷ 0.79 × absolute pressure − 1) × 10, rounded up to 0.1 m.

Good to know

Nitrox gives you longer no-deco time at the same depth. It does not let you dive deeper.
Plan with the oxygen percentage you analysed, not the one you asked for. On EAN32 to EAN40, each extra percent of oxygen moves the MOD about 1 m shallower.
A slightly leaner mix than the best mix leaves a margin. For a 30 m dive the best mix is EAN35, while EAN32 still works down to 33.7 m.
If your computer is set to air while you breathe nitrox, it counts more nitrogen than you take up. That is conservative, but it won't warn you about your MOD.

How to use the nitrox calculator

1
Pick what you want to know: MOD (how deep you can go on your gas), Best Mix (which gas suits your planned depth) or EAD (how much nitrogen you take up).
2
Enter the oxygen percentage from your tank's analysis label and choose a ppO₂ limit. The usual limit for the working part of a dive is 1.4 bar.
3
Read the result and the depth diagram. The red zone is where the oxygen in your gas becomes dangerous, so plan your dive to stay above it.

What the results mean

MOD is the deepest point where the oxygen partial pressure of your gas stays at or below the limit you chose. Going below it raises the risk of central nervous system oxygen toxicity, which can cause convulsions underwater.

Best mix is the highest oxygen percentage whose MOD still reaches your planned depth. More oxygen means less nitrogen, which gives you longer no-decompression time at the same depth.

EAD is the air depth with the same nitrogen partial pressure as your nitrox dive, so you can plan no-decompression limits with air tables.

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