What is equivalent air depth?

Equivalent air depth is the depth at which breathing air would give you the same nitrogen partial pressure as your Nitrox mix does at your actual depth. Because decompression models are driven by inert gas, an air table or planner can be used at the EAD rather than the real depth.

Does a shallower EAD mean I can dive deeper?

No. EAD only describes nitrogen loading. Your depth ceiling comes from oxygen, via maximum operating depth, and enriching the mix makes that ceiling shallower rather than deeper. EAD and MOD move in opposite directions for the same mix.

Do I still need EAD if I dive a computer?

A Nitrox-capable computer set to the analyzed mix tracks inert gas directly, so you do not convert depths by hand. EAD remains useful for understanding why Nitrox extends no-stop time, for cross-checking a plan, and for table-based planning. For example, EAN32 at 30 meters has an EAD of about 24 meters. (A Nitrox-capable computer set to the analyzed mix tracks inert gas directly, so you do not convert depths by hand. EAD remains useful for understanding why Nitrox extends no-stop time, for cross-checking a plan, and for table-based planning. For example, EAN32 at 100 feet has an EAD of about 80 feet.)

Is EAD the same as equivalent narcotic depth?

They are different questions that can share arithmetic. EAD asks about decompression and counts only nitrogen. Equivalent narcotic depth asks about impairment, and because oxygen is also narcotic many divers treat a Nitrox mix as no less narcotic than air at the same depth.

Diving guide

Equivalent Air Depth (EAD) Explained

Work out the air depth a Nitrox dive is decompression-equivalent to, and see why EAD never changes your oxygen limit.

Nitrox extends no-stop time because you breathe less nitrogen at the same depth. Equivalent air depth puts a number on that: it is the shallower depth an air diver would have to be at to absorb nitrogen as fast as you are.

What EAD actually answers

Decompression models track inert gas, not oxygen. For a recreational Nitrox mix the inert gas is nitrogen, so two dives that produce the same nitrogen partial pressure produce comparable nitrogen loading. EAD converts your real depth on a rich mix into the air depth that matches it, which lets an air table or an air-based planner be used for a Nitrox dive.

The comparison is deliberately narrow. EAD says nothing about oxygen exposure, gas supply, narcosis, or thermal stress. It answers one question — how much nitrogen — and answers nothing else.

The EAD formula

Convert depth to absolute pressure, scale by the ratio of your nitrogen fraction to the nitrogen fraction of air, then convert back to depth:

\text{EAD} = \left(\text{depth} + 10\right) \times \frac{\text{FN}_2}{0.79} - 10

\text{EAD} = \left(\text{depth} + 33\right) \times \frac{\text{FN}_2}{0.79} - 33

Where $\text{FN}_2$ is the fraction of nitrogen in your mix — 0.68 for EAN32, because the balance of a 32% oxygen mix is 68% nitrogen.

The 0.79 is the nitrogen fraction of air. Strictly, air is about 78% nitrogen plus roughly 1% argon and other trace gases; decompression practice lumps those inert gases together as 79%, which is why the same figure appears in agency tables.

Try it: Equivalent Air Depth

Compare the nitrogen loading of a Nitrox dive with an air dive.

Actual depth

Oxygen percentage

24.4 m

EAD for EAN32 at 30 m

33.8 m

MOD at 1.4 ATA

A worked example

Take EAN32 at 30 meters99 feet. Absolute pressure is 44 ATA. Scaling by 0.68 ÷ 0.79 gives 3.44 ATA of air-equivalent pressure, and converting back to depth leaves an EAD of about 24 meters80 feet.

One dive, two ways to describe it

EAN32 carries 68% nitrogen instead of 79%, so at 4 ATA it produces the nitrogen loading air would produce at about 3.4 ATA. The Nitrox dive and its shallower air equivalent are interchangeable to a decompression model — that equivalence is the entire meaning of EAD.

That is the whole benefit in one line: for decompression purposes the dive behaves like an air dive six meters19 feet shallower, which is why the no-stop time is longer. Round EAD up to the next table depth rather than down — pretending the dive was shallower than the calculation says is the unsafe direction.

Equivalent air depth reference

Raw EAD equation results for binary oxygen/nitrogen mixes, rounded to the nearest 0.1 m or 0.1 ft. Metric and imperial depths are calculated independently.

Actual depth	EAN32 EAD	EAN36 EAD	EAN40 EAD	EAN50 EAD
6 m20 ft	3.8 m12.6 ft	3.0 m9.9 ft	2.2 m7.3 ft	0.1 m0.5 ft
12 m40 ft	8.9 m29.8 ft	7.8 m26.1 ft	6.7 m22.4 ft	3.9 m13.2 ft
18 m60 ft	14.1 m47.1 ft	12.7 m42.3 ft	11.3 m37.6 ft	7.7 m25.9 ft†
24 m80 ft	19.3 m64.3 ft	17.5 m58.5 ft	15.8 m52.8 ft	11.5 m†38.5 ft†
30 m100 ft	24.4 m81.5 ft	22.4 m†74.7 ft†	20.4 m†68.0 ft†	15.3 m†51.2 ft†
36 m120 ft	29.6 m†98.7 ft†	27.3 m†90.9 ft†	24.9 m†83.2 ft†	19.1 m†63.8 ft†

† The actual depth exceeds that mix's calculated MOD at 1.4 ATA. The EAD remains nitrogen-equivalence math, not permission to use the mix at that depth.

EAD and MOD move in opposite directions

This is the trap. Enriching a mix lowers EAD, which flatters the decompression picture, while simultaneously raising oxygen partial pressure and pushing maximum operating depth shallower. EAN36 has a friendlier EAD than EAN32 at the same depth and a shallower hard ceiling.

So a shallower EAD never licenses a deeper dive. Depth is limited by oxygen; time is limited by inert gas. Confirm the ceiling with the MOD calculator before you think about no-stop time at all.

Where EAD still earns its place

A Nitrox-capable computer set to the analyzed mix tracks inert gas directly, so most divers never convert a depth by hand. EAD remains worth understanding because it explains why the computer gives you longer, it lets you sanity-check a plan before the dive, and it is still the mechanism behind table-based Nitrox planning.

It is also the honest way to see what you are spending. Using the extra no-stop time consumes the decompression margin the mix bought you. Keeping the air profile and breathing the richer mix banks that margin instead. Neither choice removes decompression risk. See no-decompression limits for what the limit itself represents.

EAD is an educational conversion for trained Nitrox divers, not a planning authority. It assumes an analyzed mix and says nothing about oxygen exposure, gas supply, or narcosis. Follow the tables, computer settings, and procedures taught by your training organization.

Sources

References and further reading

These official and specialist sources support the concepts in this guide. Always use current training materials and operational procedures for dive planning.

NOAANOAA Diving Manual: Diving for Science and Technology (6th ed.)
Reference text for diving physics, breathing gases, decompression, and oxygen exposure.
PADIWhat Is Nitrox?
Divers Alert NetworkBreathing Gases

Equivalent Air Depth (EAD) Explained

What EAD actually answers

The EAD formula

Try it: Equivalent Air Depth

A worked example

One dive, two ways to describe it

Equivalent air depth reference

EAD and MOD move in opposite directions

Where EAD still earns its place

References and further reading

Frequently Asked Questions

Related Guides

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