Equivalent Air Depth (EAD)

The air depth whose nitrogen exposure matches a nitrox dive, used to apply air tables to enriched mixes; EAN32 at 30 m has an EAD of about 24 m.

Equivalent air depth, or EAD, is the depth at which breathing air would give the same nitrogen partial pressure as your current nitrox dive. It answers a practical question: since my mix carries less nitrogen than air, how much shallower is this dive pretending to be for decompression purposes? Diving EAN32 at 30 m, for example, gives an EAD of roughly 24 m, so you could plan the dive using the 24 m row of an air table.

The formula in meters is EAD equals depth plus 10, times the nitrogen fraction divided by 0.79, minus 10. It was the standard way to use nitrox before dedicated nitrox tables and computers existed, and it still appears in nitrox courses because it makes the benefit of enriched air concrete: less nitrogen means your tissues behave as if the dive were shallower.

Modern dive computers do this continuously and invisibly once you set your mix, but understanding EAD helps you sanity check the numbers your computer displays. It also explains a planning subtlety: EAD covers only nitrogen and decompression. Oxygen exposure follows actual depth, not equivalent depth, so a nitrox dive can be limited by its MOD long before its nitrogen based no-decompression limit becomes relevant.