Gas planning reference

Minimum Gas Calculator (CAT Method)

Minimum Gas Reserve (MGR) is the amount of gas you need to safely ascend with a buddy after an emergency at depth. This calculator uses the CAT method ( Consumption × ATA × Time ) to help recreational divers estimate their reserve and plan their turn pressure accordingly. Most divers are unfamiliar with the CAT method unless they have taken GUE training like Fundamentals.

The CAT formula accounts for solving a problem at depth and making a controlled ascent, but it does not include a safety stop. While safety stops are recommended for every dive, they are not required in an out-of-gas scenario. This tool assumes a worst-case situation and focuses on the minimum you truly need to surface alive, not what’s ideal under perfect conditions.

Adjust the options below to reflect your dive plan, then choose a turn pressure method to match your comfort and environment.

Set Your Dive Parameters

Select Depth:

Your RMV (cuft/min):

Include Buddy:

Ascent Rate to Half Depth (ft/min):

Ascent Rate from Half Depth to Surface (ft/min):

Problem Resolution Time (min):

Tank Type:

Turn Pressure Method:

The highlighted row is your selected depth. Red rows show zero available bottom time and a plan that needs adjustment.

Scroll horizontally to see all reserve and turn-pressure columns.

Selected Depth Summary

Selected Depth (ft): -
Minimum Gas Reserve (cuft): -
Minimum Gas Reserve (PSI): -
Turn Pressure (PSI): -
Estimated Max Bottom Time (minutes): -
Selected Planning Method: -

Minimum gas reserve and turn pressure by depth
Depth (ft)	Min Gas (cuft)	Min Gas (PSI)	Usable Gas (cuft)	Usable Gas (PSI)	Turn Pressure (PSI)	Estimated Max Bottom Time (min)
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How This Calculator Works

This calculator estimates the minimum gas you and a buddy would need to safely ascend from depth using the CAT method (Consumption × ATA × Time). It factors in your breathing rate, average depth pressure during ascent, ascent rate, and any problem-resolution time you set. The result is converted into PSI based on your selected tank and rounded up to the nearest 50 psi (with a 500 psi minimum). From this reserve, the calculator determines your usable gas, turn pressure (depending on the chosen rule), and an estimated maximum bottom time under those conditions.

Interpreting the Table

Use the Turn Pressure column to decide when to start back or ascend. Estimated Max Bottom Time shows how much time you have at your selected depth once descent gas and reserve are accounted for. Rows highlighted in red indicate zero available bottom time under your inputs, which signals a plan that needs adjustment.