Oxygen Partial Pressure (ppO2) Calculator
Enter the oxygen fraction of your breathing gas and a depth to see the oxygen partial pressure it delivers. ppO2 rises with ambient pressure, so the same nitrox mix that is comfortable shallow can exceed the 1.4 ata working limit deeper. The tool shows both the ambient pressure in ata and the resulting ppO2, and flags whether it stays within 1.4 ata.
How to calculate oxygen partial pressure
- Type the oxygen percentage of your gas in the Oxygen percentage field, such as 21 for air, 32 for EAN32 or 36 for EAN36.
- Pick Metres or Feet from the Depth units menu.
- Enter the depth in the Depth field (any value greater than zero).
- Read the Oxygen partial pressure card in ata and the green Within or red Over 1.4 ata label.
- Check the Ambient pressure card for the ata at that depth, then use Copy to grab the summary line.
Examples
EAN32 at 30 m (metric)
Oxygen 32%, units Metres, depth 30
Ambient 4 ata, ppO2 1.28 ata, within 1.4 limit
EAN32 at 40 m (over the limit)
Oxygen 32%, units Metres, depth 40
Ambient 5 ata, ppO2 1.6 ata, over 1.4 limit
EAN36 at 66 ft (imperial)
Oxygen 36%, units Feet, depth 66
Ambient 3 ata, ppO2 1.08 ata, within 1.4 limit
Frequently asked questions
What is oxygen partial pressure in diving?
ppO2 is the portion of the total breathing pressure made up by oxygen. At depth the total ambient pressure rises, so the ppO2 of a fixed mix rises with it. A high ppO2 is what drives central nervous system oxygen toxicity risk.
How does this calculator compute ppO2?
It first finds ambient pressure: ata is depth in metres divided by 10 plus 1, or depth in feet divided by 33 plus 1. Then ppO2 equals the oxygen percentage divided by 100, times that ata. Air at 30 m gives 0.21 times 4 = 0.84 ata.
Why does it use 10 m and 33 ft per atmosphere?
Those are the standard seawater approximations for one atmosphere of pressure. Freshwater is slightly less dense, so a real freshwater atmosphere sits nearer 10.3 m, but the 10 m and 33 ft rounding is the conservative convention taught in nitrox courses.
What ppO2 limit does the tool check?
It flags whether your ppO2 is at or below 1.4 ata, the working limit taught for recreational diving. The exposure value of 1.6 ata that many agencies reserve for short contingency or deco use is not treated as a separate pass, so anything above 1.4 shows as over.
How do I find the maximum operating depth from this?
Increase the depth until the ppO2 reaches your chosen ceiling. The depth just before it crosses 1.4 ata is the MOD for that ceiling. For a direct answer, the related nitrox MOD calculator solves the depth for you.
What numbers can I enter?
Oxygen must be greater than 0 and at most 100 percent, and depth must be greater than zero. Results round to nine internal digits and display to two decimals, so 4 ata shows as 4 and 1.28 ata shows as 1.28.
What happens if ppO2 gets too high?
A high ppO2 raises the risk of central nervous system oxygen toxicity, which can trigger convulsions underwater and is frequently fatal. Keeping ppO2 within the planned ceiling, and treating 1.6 ata as an absolute exposure limit, is why every mix has a maximum operating depth.
Is my data private?
Yes. The calculation runs entirely in your browser with JavaScript. No oxygen percentage, depth or result is uploaded to a server, so nothing you type leaves your device.
Can I rely on this tool instead of training?
No. It is a training and planning aid that computes ppO2 and ambient pressure only. Get certified, analyse every cylinder with an oxygen analyser, follow your training and defer to your dive computer and tables in the water.
Learn more
- ppO2, oxygen toxicity and the 1.4 and 1.6 limits
How oxygen partial pressure scales with depth, why nitrox raises toxicity risk faster than air, and what the 1.4 and 1.6 ata limits mean.
Related tools
Nitrox MOD Calculator
Find the maximum operating depth of any nitrox mix in metres and feet. Set the oxygen percentage and your ppO2 limit, default 1.4 ata. Free planning aid.
Best Nitrox Mix Calculator
Find the richest nitrox mix for a planned depth in metres or feet. Enter your target depth and ppO2 limit to get the best oxygen percentage for the dive.
Equivalent Air Depth Calculator
Convert a nitrox dive to its equivalent air depth in metres or feet. Enter the oxygen percentage and depth to read the EAD for table and computer planning.
Scuba Air Consumption Calculator
Work out your surface air consumption rate from a dive. Enter start and end pressure, time and depth to get a SAC rate in psi or bar per minute for planning.