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Dive Planning

Rock Bottom Gas Calculator

Calculate the minimum gas a team needs to share one supply and ascend from the deepest point of a dive, then convert it to a reserve pressure for your cylinder.

Dive and team

The deepest point of the dive and how the team breathes under stress.

m

Allowed range: 6 to 60 m.

L/min

Allowed range: 15 to 70 L/min.

divers

Allowed range: 1 to 4 divers.

Exit profile

These assumptions are the safety guidance. Use the values your training organization teaches for the environment you dive.

min

Allowed range: 0 to 5 min.

m/min

Allowed range: 3 to 18 m/min.

m

Allowed range: 0 to 12 m.

min

Allowed range: 0 to 10 min.

Cylinder

The gas volume is the same for any cylinder; the reserve pressure depends on the one each diver carries.

L

Allowed range: 5 to 20 L.

Tank size presets
Plan the dive above this reserve in the gas planner

Emergency floor only

Rock bottom is the gas that must still be in the cylinder when the ascent begins from the deepest point. It is not a turn pressure, does not include the planned dive, and cannot model decompression obligations, overhead environments, currents, equipment failures beyond a single shared supply, or every emergency. Apply the method and reserves taught by your training organization.
Segment breakdown
  • Solve the problem at depth
    1 min
    240 L
  • Ascend to the stop
    2.8 min
    458 L
  • Hold the stop
    3 min
    270 L
  • Ascend to the surface
    0.6 min
    42 L
About rock bottom

Rock bottom, or minimum gas, is the reserve a team needs for a gas-sharing emergency at the most demanding point of the dive. Every segment is charged at its ambient pressure, so the deepest minutes are the most expensive.

V=n RMV∑iti PˉiV = n \, \text{RMV} \sum_{i} t_i \, \bar{P}_i

Where

VV
minimum gas for the team, as surface volume
nn
divers breathing from the reserve
RMV\text{RMV}
stressed surface breathing rate per diver
tit_i
minutes in each exit segment
Pˉi\bar{P}_i
mean ambient pressure of that segment (ATA)

Reserve pressure divides that volume by the cylinder's capacity and is rounded up to the next 5 bar so it can be read on a gauge.

Result

95 bar reserve

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