Nitrox and maximum operating depth
The depth a mix stops being safe, the partial pressure of oxygen you are actually breathing, and the best blend for a planned depth.
Free to use, no account needed. The calculator loads below.
Maximum operating depth is an oxygen limit
The maximum operating depth of a nitrox blend is the depth at which the partial pressure of the oxygen in it reaches your chosen limit. Past that depth you are into the region where central-nervous-system oxygen toxicity becomes a real risk, and the first symptom can be a convulsion underwater.
This is the trade every nitrox diver makes. More oxygen means less nitrogen, which means longer no-stop times. It also means a shallower ceiling. EAN36 gives you a generous bottom time at 20 metres and has no business at 35.
1.4 or 1.6 bar
1.6 bar is the accepted hard ceiling from the NOAA oxygen exposure limits. 1.4 bar is the working limit that agencies plan recreational dives to, and the gap between them is the margin you keep for exertion, cold, carbon dioxide retention and a depth excursion you did not plan.
Both are offered here because the difference between them is the entire point of the calculation. Plan to 1.4. Understand 1.6 as the number you do not cross, not as a target.
Equivalent air depth, and best mix
Equivalent air depth answers the question your tables were built for: what depth would load me with nitrogen the way this mix does at this depth? It is always shallower than your real depth on nitrox, and it is how you convert a nitrox dive into an air plan.
Best mix runs the calculation the other way. Give it a depth and a ppO2 limit and it returns the richest blend that stays legal there, which is the blend that buys you the most bottom time at that depth.
Common questions
What is the maximum operating depth for EAN32?
About 33 metres at a 1.4 bar working limit, and about 40 metres at the 1.6 bar hard ceiling. Run the numbers above to see both, and plan to the working limit.
Does nitrox let me dive deeper?
No, the opposite. Nitrox extends your no-stop time at recreational depths, but its oxygen content gives it a shallower maximum operating depth than air. Deeper diving needs less oxygen in the mix, not more, which is where trimix comes in.
What is equivalent air depth used for?
It converts a nitrox dive into the air dive that would load your tissues the same way, so you can plan a nitrox dive on air tables or compare it with an air profile.
Why do I need to analyse my own cylinder?
Because the blend in the tank is the one you breathe, not the one on the label. Every nitrox dive starts with you personally analysing the mix and recording it, and the maximum operating depth you plan comes from that reading.
The rest of it lives in the app
The app keeps your analysed mixes with the dive, warns you when a planned depth would exceed the ppO2 limit for the gas you logged, and tracks your CNS and OTU loading across a day of diving.