Equivalent Narcotic Depth (END)

END estimates the air depth with the same narcotic gas partial pressure as your breathing mix at a given depth. Choose whether oxygen is considered narcotic (common practice varies); nitrogen is always narcotic and helium is not.

Enter depth and mix to compute END.

How to use the END calculator

Enter your planned depth along with your mix's O₂% and He% — nitrogen fills the remainder automatically. Tick the checkbox if you want oxygen counted as narcotic (conventions vary by agency), then hit Compute.

The result is the depth on air that would produce the same narcotic partial pressure as your trimix or heliox mix at your entered depth — useful for checking a gas plan against your own or your agency's END limit before a dive.

FAQ

How do you calculate equivalent narcotic depth?

END compares the narcotic partial pressure of your actual breathing mix at depth to what a diver breathing air would experience. The narcotic fraction of your mix (nitrogen, and oxygen if you choose to count it as narcotic) is multiplied by the absolute pressure at your depth, then divided by air's narcotic fraction (0.79, or 1.0 if counting oxygen) to get an equivalent pressure — which converts back to a depth using 10 m per bar. This calculator does that conversion directly from your entered depth, O2%, and He%.

Is oxygen narcotic?

It's debated. Nitrogen is always treated as narcotic; helium is treated as non-narcotic. Oxygen's narcotic effect is smaller and less certain, so different agencies and instructors take different positions — some count it, some don't, particularly at the OC2/high-PO2 end. This calculator lets you toggle whether oxygen counts as narcotic so you can match whichever convention your training follows.

What's a safe END limit for trimix diving?

Many trimix courses teach keeping END no deeper than around 30 m (100 ft) air-equivalent, treating that as roughly the point where narcosis starts meaningfully affecting judgment and task performance for most divers — but individual susceptibility varies, and your agency's own standards take precedence over any single rule of thumb.

Equivalent Narcotic Depth (END)

END estimates the air depth with the same narcotic gas partial pressure as your breathing mix at a given depth. Choose whether oxygen is considered narcotic (common practice varies); nitrogen is always narcotic and helium is not.

Enter depth and mix to compute END.

How to use the END calculator

Enter your planned depth along with your mix's O₂% and He% — nitrogen fills the remainder automatically. Tick the checkbox if you want oxygen counted as narcotic (conventions vary by agency), then hit Compute.

The result is the depth on air that would produce the same narcotic partial pressure as your trimix or heliox mix at your entered depth — useful for checking a gas plan against your own or your agency's END limit before a dive.

FAQ

How do you calculate equivalent narcotic depth?

END compares the narcotic partial pressure of your actual breathing mix at depth to what a diver breathing air would experience. The narcotic fraction of your mix (nitrogen, and oxygen if you choose to count it as narcotic) is multiplied by the absolute pressure at your depth, then divided by air's narcotic fraction (0.79, or 1.0 if counting oxygen) to get an equivalent pressure — which converts back to a depth using 10 m per bar. This calculator does that conversion directly from your entered depth, O2%, and He%.

Is oxygen narcotic?

It's debated. Nitrogen is always treated as narcotic; helium is treated as non-narcotic. Oxygen's narcotic effect is smaller and less certain, so different agencies and instructors take different positions — some count it, some don't, particularly at the OC2/high-PO2 end. This calculator lets you toggle whether oxygen counts as narcotic so you can match whichever convention your training follows.

What's a safe END limit for trimix diving?

Many trimix courses teach keeping END no deeper than around 30 m (100 ft) air-equivalent, treating that as roughly the point where narcosis starts meaningfully affecting judgment and task performance for most divers — but individual susceptibility varies, and your agency's own standards take precedence over any single rule of thumb.