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Calcimator

Trimix Blend Calculator

Calculate MOD, Equivalent Narcotic Depth (END), partial pressures, and hypoxic safety for Trimix gas blends used in technical deep diving.

Inputs

%
%

Results

MOD (metres)

56.7

END (metres)

35.5

MOD (feet)186
END (feet)116
Nitrogen (%)44
ppO2 at depth1.47
ppN2 at depth3.08
ppHe at depth2.45
Hypoxic at surface?0
Min switch depth (m)0
How to Use This Calculator
  1. Enter the oxygen percentage in your Trimix blend (e.g., 21% for normoxic, lower for hypoxic mixes).
  2. Input the helium percentage — helium replaces nitrogen to reduce narcosis at depth.
  3. Set your planned maximum depth in meters.
  4. Set your ppO2 limit in bar (1.4 for bottom gas, 1.6 for decompression).
  5. Read MOD in meters to confirm your dive plan stays within safe oxygen limits.
  6. Check END (Equivalent Narcotic Depth) in meters — ideally keep END below 30 m to minimize narcosis risk.

How the result changes with Oxygen (%)

Oxygen (%)MOD (metres)END (metres)
1583.335.5
3826.835.5
6711.336
919.440.6

What each input means

Oxygen (%)
Oxygen percentage. Below 18 % is hypoxic trimix.
Helium (%)
Helium percentage. Reduces narcosis and density.
Planned depth (m)
Maximum planned depth in metres.
ppO2 limit (bar)
Maximum partial pressure of oxygen (1.4 recreational, 1.6 deco).

What each result means

MOD (metres)
Maximum Operating Depth where ppO2 reaches your limit.
MOD (feet)
Maximum Operating Depth in feet.
END (metres)
Equivalent Narcotic Depth — effective depth for narcosis risk.
END (feet)
Equivalent Narcotic Depth in feet.
Nitrogen (%)
Balance nitrogen percentage.
ppO2 at depth
Partial pressure of oxygen at planned depth.
ppN2 at depth
Partial pressure of nitrogen at planned depth.
ppHe at depth
Partial pressure of helium at planned depth.
Hypoxic at surface?
1 = mix is hypoxic at surface (ppO2 < 0.16), 0 = safe to breathe at surface.
Min switch depth (m)
If hypoxic, the shallowest depth where this mix is safe to breathe.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Oxygen (%) = 21, Helium (%) = 35, Planned depth (m) = 60, ppO2 limit (bar) = 1.4 = 4 input(s) provided
  2. Calculate MOD
    MOD = (ppO2max / fO2 - 1) * 10
    56.7 = 56.7
  3. Calculate END
    END
    35.5 = 35.5
  4. Calculate MOD
    MOD = modM * 3.281
    186 = 186
  5. Calculate END
    END = endM * 3.281
    116 = 116

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.

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