Best Nitrox Mix Calculator

What is the optimal Nitrox mix?

The optimal Nitrox blend, for a certain depth, is the mix that has the least amount of nitrogen possible (and more oxygen), without exceeding the safe ppO2 limit for oxygen toxicity. Using the optimal nitrox mix for a certain depth will minimize your nitrogen exposure and allow you to extend your bottom time by increasing your NDL (No Decompression Limit).

The blend that meets both of those criterias (minimizing nitrogen and not exceesind the safe ppO2) is the one that, when breathed at that depth, has a ppO2 that equals the limit (1.4 atm for recreational diving). Each depth has its own optimal nitrox blend.

How to calculate the best Nitrox mix

As mentionned previously, the optimal mix for a certain depth is the mix which, at that depth, has an Oxygen partial pressure of 1.4 atm. Finding the optimal nitrox mix for a certain depth is the inverse of calculating the MOD (Maximum Operating Depth). To calculate the optimal Nitrox blend for a specific depth, the formula is:

FO2 = 14 / (Depth + 10) ( with depth in meters)

FO2 = 46 / (Depth + 33) (with depth in feet)

With these formula, the result (FO2) is expressed as a fraction (between 0 and 1), if you want to get the result as a percentage, you need to multiply the result by 100.

You may notice that there is a 14 in the formula (46 in the formula using feet), this comes from multiplying the maximum tolerated ppO2 (1.4) by 10 (in the formula using feet, we multiply 1.4 by 33, which is where the 46 comes from). If you would like to tweak the maximum ppO2 allowed, you can use the following formulas instead:

FO2 = (ppO2 × 10) / (Depth + 10) ( with depth in meters)

FO2 = (ppO2 × 33) / (Depth + 33) (with depth in feet)

The following table shows the optimal nitrox blend for various depths:

Depth	Optimal mix (O2%)
18m	50%
20m	46%
22m	43%
24m	41%
26m	38%
28m	36%
30m	35%
32m	33%
34m	31%
36m	30%
38m	29%
40m	28%