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MOD / EAD / END

This page groups four related gas-depth calculators: MOD, Best Mix, EAD, and END. Together they cover the most common nitrox and trimix planning questions: maximum safe depth, ideal mix selection, and narcosis equivalency.

Free Tool

The MOD / EAD / END calculator is completely free and does not require an account.

MOD: Maximum Operating Depth​

The MOD calculator tells you the deepest you can safely go on a given gas mix before exceeding your maximum partial pressure of oxygen (PPO2) limit.

Inputs:

  • O2 percentage: the oxygen fraction of your breathing mix (21--100%)
  • Max PPO2: the maximum acceptable partial pressure of oxygen (in bar). This value is pre-loaded from your diver profile settings.
  • Altitude: elevation of the dive site (affects ambient pressure calculations)
  • Water type: fresh or salt water (affects water density and pressure at depth)

Output:

  • Maximum safe depth in both meters and feet

Best Mix​

The Best Mix calculator works in reverse: given a target depth and PPO2 limit, it tells you the ideal nitrox mix to use.

Inputs:

  • Target depth: the depth you plan to dive
  • Max PPO2: your PPO2 limit

Output:

  • Recommended O2 percentage
  • Mix classification: standard air, EAN (enriched air nitrox), or hypoxic

EAD: Equivalent Air Depth​

The EAD calculator compares the nitrogen narcosis effect of a nitrox mix at depth to breathing regular air at a shallower depth. This helps nitrox divers understand the effective nitrogen exposure of their dive.

Inputs:

  • Depth: actual dive depth
  • O2 percentage: the oxygen fraction of the mix

Output:

  • Equivalent air depth in meters and feet

For example, diving on EAN32 at 30 m gives an EAD of roughly 24 m, meaning the nitrogen narcosis is equivalent to breathing air at 24 m.

END: Equivalent Narcotic Depth​

The END calculator extends the EAD concept to trimix diving by accounting for helium, which is non-narcotic. It supports two modes: Nitrox (no helium) and Trimix (O2 + He + N2).

Inputs:

  • Depth: actual dive depth
  • O2 percentage: oxygen fraction
  • He percentage: helium fraction (trimix mode only; nitrogen is calculated automatically)
  • Narcotic O2 toggle: whether to treat oxygen as narcotic

Output:

  • Equivalent narcotic depth in meters and feet

In trimix mode, helium replaces some of the nitrogen in the mix, reducing narcosis at depth. The narcotic O2 toggle lets you choose whether oxygen contributes to the narcotic effect; this is debated in diving physiology, so both approaches are supported.