EAD: equivalent air depth
With nitrox you breathe less nitrogen. The EAD is the depth to read in your air table or your computer set to air.
Your dive
Planned maximum depth and analysed mix.
The PpO2 limit you use
This mix at other depths
Tap a row to use it.
PpO2 in orange: above 1.4 bar. In red: above 1.6 bar, forbidden.
| Depth | EAD (table) | MN90 row | PpO2 |
|---|---|---|---|
Depth to read in the air table
25m
Exact value: 24.4 m, rounded up to the metre.
With Nx32 at 30 m, you breathe as much nitrogen as on air at 24.4 m.
Mix usable at 30 m
PpO2 of 1.28 bar, under your 1.4 bar limit (max depth 33 m).
Oxygen
Bottom PpO2 and depths not to exceed.
Max depths rounded down to the metre.
Understanding the calculation
1. Absolute pressure
Count 1 bar of atmosphere plus 1 bar for every 10 m of water.
P = depth ÷ 10 + 1
2. EAD
We look for the depth where air (79 % nitrogen) gives the same nitrogen pressure as your nitrox at your depth.
EAD = (depth + 10) × (1 − FO2) ÷ 0.79 − 10
Example: EAN32 at 30 m → 40 × 0.68 ÷ 0.79 − 10 = 24.4 m, so 25 m in the table. Always round up to the metre to stay on the safe side.
And in the MN90 table?
The table does not list every depth. Take the row equal to or just deeper than the EAD: 25 m gives the 25 m row, 23 m also gives the 25 m row.
3. PpO2 and maximum depth
PpO2 = FO2 × P
Max depth = (PpO2 limit ÷ FO2 − 1) × 10
The maximum depth is rounded down to the metre. Example: EAN32 at 1.4 bar → 33.75 m, so 33 m.
Key points
- The EAD only applies if the PpO2 stays within your limit. Beyond it, the risk of oxygen toxicity comes before nitrogen.
- Calculated with 10 m = 1 bar, at sea level. In a lake the real pressure is slightly lower, so the result stays on the safe side. At altitude, use a dedicated tool.
- The EAD only counts nitrogen. Oxygen is narcotic too: for narcosis, the EAD is optimistic.
- Diving nitrox with an air table, without using the EAD, keeps an extra margin.
- A teaching tool: it replaces neither your nitrox training nor your computer.
Understanding EAD
What is the EAD?
The EAD (Equivalent Air Depth) is the depth at which air would make you breathe as much nitrogen as your nitrox at your real depth. EAN32 holds 68 % nitrogen instead of 79 %: at 30 m you breathe as much nitrogen as on air at 24.4 m. That depth, rounded up to the metre, is what you read in an air table.
Reading the MN90 table with nitrox
The French MN90 table does not list every depth: take the row equal to or just deeper than the EAD. With a 25 m EAD, use the 25 m row; with 23 m, also the 25 m row. Then read your time and stops as for an air dive, with more no-stop time than at your real depth.
Oxygen comes before nitrogen
Less nitrogen, but more oxygen: the EAD only makes sense if your ppO2 stays within your limit. Before looking at the EAD, check your maximum depth with the MOD tool and your ppO2 on the bottom and at the stops with the PpO2 tool. To choose the most useful mix for a given depth, use the best mix tool.
A ready-made link for your students
The tool accepts parameters in the address: add ?d=30&o2=32&lim=1.4 to the end of the link to open it prefilled with 30 m, EAN32 and a 1.4 bar limit. Handy for an instructor preparing a nitrox exercise.
Frequently asked questions
How do you calculate the EAD?
EAD = (depth + 10) × (1 − FO2) ÷ 0.79 − 10. Example: EAN32 at 30 m → 40 × 0.68 ÷ 0.79 − 10 = 24.4 m, rounded up to 25 m.
What is the EAD of EAN32 at 30 m?
24.4 m, so 25 m in the table. You breathe 2.72 bar of nitrogen instead of 3.16 bar on air, 13.9 % less.
Why round the EAD up?
To stay on the safe side: a deeper EAD gives less no-stop time in the table. It is the opposite of the MOD, which is rounded down.
Does the EAD reduce narcosis?
Not really: the EAD only counts nitrogen, and oxygen is narcotic too. For narcosis, the EAD is therefore optimistic.