Calculator
EAD calculator — Equivalent air depth for Nitrox
Equivalent air depth (EAD) is the depth at which air would have the same nitrogen partial pressure as your Nitrox mix at the actual depth. It's the bridge that lets you use air NDL tables for Nitrox dives — the lower the EAD, the more bottom time you get.
How EAD is calculated
EAD comes from equating nitrogen partial pressures: the dive's actual N₂ pressure (FN₂ × P_ambient) must match the equivalent air depth's N₂ pressure (0.79 × P_equivalent).
EAD (m) = ((1 − FO₂) ÷ 0.79) × (D + 10) − 10 FO₂ oxygen fraction of the Nitrox mix D actual depth in metres of seawater
Worked example: EAN36 at 30 m. FN₂ = 0.64. EAD = ((1 − 0.36) / 0.79) × (30 + 10) − 10 ≈ 24 m. Use the 24 m row of an air table to look up NDL.
When EAD is appropriate
EAD only addresses nitrogen loading. It doesn't account for oxygen exposure (CNS / OTU) or gas density. For modern dive computers running real-time tissue tracking, EAD is mostly a teaching aid — the algorithm uses the actual gas. EAD is still the standard tool for teaching Nitrox theory and for cross-checking computer behavior on simple square profiles.
Frequently asked questions
- What's the EAD of EAN32 at 30 m?
- About 26 m. EAN36 at 30 m drops further, to ~24 m, which is why EAN36 was the recreational sweet spot for many years.
- Does EAD apply to Trimix?
- Not directly. For Trimix you generally use END (equivalent narcotic depth) for narcosis and the actual depth for tissue loading via a computer. EAD is a Nitrox concept built around nitrogen-only inert gas.
- Why does my EAD differ from my computer's?
- Most computers don't display EAD — they integrate tissue compartments directly using the gas in use. The EAD here uses the textbook formula assuming sea-level salt water.
- Is EAD safer than the actual depth?
- EAD is shallower than the dive's actual depth because Nitrox has less nitrogen than air. NDL is longer at the EAD; you still respect the actual depth's MOD and any oxygen-exposure limits.