Nitrox Calculator
Planning a dive on enriched air? Use this calculator to find your Maximum Operating Depth (MOD), Equivalent Air Depth (EAD), and oxygen partial pressure for any nitrox mix from EAN21 to EAN40.
Gas Mix & Depth
At 30m with a 1.4 ppO2 limit, the optimal mix is EAN35.
Results
What is Nitrox?
Nitrox, also called Enriched Air Nitrox (EANx), is a breathing gas with a higher percentage of oxygen than regular air (21% O2). The most common mixes are EAN32 (32% oxygen) and EAN36 (36% oxygen). By reducing the nitrogen fraction, nitrox extends no-decompression limits and can reduce post-dive fatigue.
Understanding the Calculations
Maximum Operating Depth (MOD)
The MOD is the deepest you can safely dive on a given nitrox mix before the partial pressure of oxygen becomes dangerously high. The recreational limit is a ppO2 of 1.4 bar, with 1.6 bar as the absolute maximum for decompression stops only. The formula is: MOD = (ppO2 / fO2 - 1) x 10.
Equivalent Air Depth (EAD)
EAD tells you the depth at which air would have the same nitrogen partial pressure as your nitrox mix at your actual depth. This lets you use standard air dive tables with nitrox. A lower EAD means less nitrogen loading and longer no-decompression limits.
Partial Pressure of Oxygen (ppO2)
The ppO2 increases with depth according to Dalton's Law. Above 1.4 bar, the risk of central nervous system (CNS) oxygen toxicity rises significantly. Symptoms can include tunnel vision, ringing ears, nausea, twitching, and seizures - any of which can be fatal underwater.
CNS Toxicity Limits
NOAA publishes maximum single-exposure time limits based on ppO2 levels. At 1.6 bar ppO2, the limit is just 45 minutes. These limits are cumulative over a 24-hour period, so multiple dives on nitrox require tracking total CNS loading.