Calculate equivalent air depth from total depth and nitrogen fraction, or solve for depth or FN, with results in ft, m, cm, or in.

Compare nitrogen partial pressure with air at another depth.

Nitrogen-pressure comparison only. This does not check oxygen exposure, maximum operating depth, decompression or ascent limits. Use analyzed gas and approved dive-planning tools.

Related Calculators

Equivalent Air Depth Formula

The equivalent air depth, or EAD, estimates the air depth that would create the same nitrogen partial pressure as a nitrox mix at a given actual depth. This calculator uses feet as the base unit, applies the EAD formula, then converts the answer to your selected unit.

EAD = ((D + 33) × FN / 0.79) - 33
D = ((EAD + 33) × 0.79 / FN) - 33
FN = ((EAD + 33) × 0.79) / (D + 33)
  • EAD = equivalent air depth, in feet before any unit conversion
  • D = actual total depth, in feet before any unit conversion
  • FN = fraction of nitrogen in the breathing gas, such as 0.68 for EAN32
  • 0.79 = approximate fraction of nitrogen in air
  • 33 = sea-level pressure convention of 33 feet of seawater per atmosphere; all displayed length units convert this same model

If you enter total depth and fraction of nitrogen, the calculator solves for EAD. If you enter EAD and fraction of nitrogen, it solves for total depth. If you enter total depth and EAD, it solves for the nitrogen fraction. Choose the nitrogen-content unit explicitly: Fraction for 0.68, or Percent for 68.

Common Nitrox Nitrogen Fractions

For nitrox, the nitrogen fraction is usually found by subtracting the oxygen fraction from 1.

Gas Mix Oxygen Fraction Nitrogen Fraction to Enter
Air 0.21 0.79
EAN32 0.32 0.68
EAN36 0.36 0.64
EAN40 0.40 0.60

Sample EAD Values in Feet

Actual Depth EAN32, FN 0.68 EAN36, FN 0.64 EAN40, FN 0.60
60 ft 47.05 ft 42.34 ft 37.63 ft
80 ft 64.27 ft 58.54 ft 52.82 ft
100 ft 81.48 ft 74.75 ft 68.01 ft

Example Problems

Example 1: Find EAD from depth and nitrogen fraction

You are diving to 80 ft on EAN32. The nitrogen fraction is 0.68.

EAD = ((80 + 33) × 0.68 / 0.79) - 33
EAD = 64.27 ft

The equivalent air depth is about 64.27 ft.

Example 2: Find nitrogen fraction from depth and EAD

You have an actual depth of 100 ft and an equivalent air depth of 74.75 ft.

FN = ((74.75 + 33) × 0.79) / (100 + 33)
FN = 0.64

The nitrogen fraction is about 0.64, which corresponds to a gas with about 36% oxygen if it is a simple nitrox mix.

FAQ

What does equivalent air depth mean?

Equivalent air depth is the depth on air that gives the same nitrogen partial pressure as your selected breathing gas at the actual depth. A lower EAD usually means lower nitrogen loading than breathing air at the same actual depth.

Can I enter the nitrogen fraction as a percent?

Yes. You can enter nitrogen as a decimal or a percent. For example, EAN32 has 68% nitrogen, so you can enter either 0.68 or 68. Choose Fraction for 0.68 or Percent for 68. The unit selector makes the distinction explicit.

Is EAD the same as oxygen exposure?

No. EAD is about nitrogen exposure only. It does not check oxygen partial pressure, maximum operating depth, decompression requirements, ascent rate, or other dive-planning limits. You still need to use appropriate dive tables, a dive computer, and the analyzed gas mix for the dive. See the U.S. Navy Diving Manual, section 10-2.1, and NOAA nitrox safety guidance, section 6.6.5.