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Gas Planning Calculator

Plan your gas supply using SAC rate, depth, and time. Calculates consumption at depth (Boyle's Law), maximum bottom time, turn pressure, and reserve adequacy.

Inputs

Results

Consumption at depth (L/min)

52.5

Max bottom time (min)

33.2

Gas needed (litres)2,100
Turn pressure (bar)129
Remaining pressure (bar)18
Gas sufficient?0
Sufficient with ascent?0
How to Use This Calculator
  1. Enter your Surface Air Consumption (SAC) rate in L/min — if unknown, use 15–20 L/min as a starting estimate.
  2. Input your planned maximum depth in meters and planned bottom time in minutes.
  3. Set your tank volume in litres and fill pressure in bar (standard fills are 200–207 bar).
  4. Enter your minimum reserve pressure in bar — typically 50 bar to reach the surface safely.
  5. Read Consumption at Depth (L/min) and Max Bottom Time to verify your tank has enough gas.
  6. Check Gas Sufficient? — if 0, either reduce planned depth/time or use a larger tank.

How the result changes with SAC rate (L/min)

SAC rate (L/min)Consumption at depth (L/min)Max bottom time (min)
8.529.858.6
1759.529.3
289817.8
37129.513.5

What each input means

SAC rate (L/min)
Surface Air Consumption in litres per minute at 1 ATA. Typical range: 12-20 L/min.
Depth (m)
Planned maximum depth in metres.
Planned time (min)
Planned bottom time in minutes.
Tank volume (L)
Internal tank volume in litres. AL80 = 11.1 L, Steel 80 = 11.1 L, AL63 = 9.0 L.
Fill pressure (bar)
Starting tank pressure in bar. Standard fill is 200-207 bar.
Reserve pressure (bar)
Minimum reserve pressure to surface with. Typical: 50 bar.

What each result means

Consumption at depth (L/min)
Your air consumption rate at the planned depth (SAC x ATA).
Gas needed (litres)
Total gas required for the planned bottom time at depth.
Max bottom time (min)
Maximum time you can stay at depth with usable gas.
Turn pressure (bar)
Pressure at which to start your ascent (rule of thirds).
Remaining pressure (bar)
Tank pressure remaining after the planned dive (before ascent).
Gas sufficient?
1 = yes, gas supply covers planned bottom time plus reserve. 0 = no.
Sufficient with ascent?
1 = yes, including ascent + 3 min safety stop. 0 = no.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    SAC rate (L/min) = 15, Depth (m) = 25, Planned time (min) = 40, Tank volume (L) = 11.1 = 6 input(s) provided
  2. Calculate Consumption at depth
    Consumption at depth = sacLpm * ata
    52.5 = 52.5
  3. Calculate Max bottom time
    Max bottom time = usableGasL / consumptionAtDepth
    33.2 = 33.2
  4. Calculate Gas needed
    Gas needed = consumptionAtDepth * plannedTimeMin
    2100 = 2100
  5. Calculate Turn pressure
    Turn pressure = fillBar - (fillBar - reserveBar) / 2
    129 = 129

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

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