Equivalent Air Depth (EAD):
What It Is and How to Calculate

If you're diving with Nitrox, you've probably heard of Equivalent Air Depth (EAD). It's a simple concept that lets you compare your Nitrox dive to a similar dive on air—and understand how much less nitrogen you're absorbing.

What Is Equivalent Air Depth (EAD)?

EAD is the depth at which you'd absorb the same amount of nitrogen if you were breathing air instead of Nitrox. In the modern era of dive computers, it is not particularly useful except at a conceptual level to help understanding why Nitrox gives you more NDL than air (21%)

How to Calculate EAD

The formula is:

\[ \text{EAD} = (\text{Depth} + 33) \times \left(\frac{F_{N_2}}{0.79}\right) - 33 \]

Where:

• F_N₂ = fraction of nitrogen in your gas
• Depth = actual depth in feet
• 0.79 = fraction of nitrogen in air

Example (EAN32 at 80 ft):

• F_N₂ = 1 − 0.32 = 0.68
• \(\text{EAD} = (80 + 33) \times \left(\frac{0.68}{0.79}\right) - 33\)
• \(\text{EAD} = 113 \times 0.86076 - 33\)
• \(\text{EAD} \approx 97.27 - 33 = \textbf{64.27 ft}\)

So diving EAN32 at 80 ft gives the same nitrogen exposure as air at 64 ft.

For now, just remember:

• Calculating EAD helps compare your dive to an “air equivalent” for nitrogen exposure.
• Modern dive computers may make it less essential—but it’s a powerful planning concept.
• Nitrox doesn’t reduce narcosis—it only reduces nitrogen.
• Narcosis depends on depth, gas, CO₂ buildup, and personal factors.