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
When calculating Estimated Max Bottom Time, we assume a constant descent rate of 45ft per minute. We then take the turn pressure and calculate how much bottom time you will have with the given depth consumption rate. If it is zero or below, we flag it as dangerous with a row of red.
The diver uses all available gas except for the Minimum Gas Reserve.
| Depth (ft) | Min Gas (cuft) | Min Gas (PSI) | Usable Gas (cuft) | Usable Gas (PSI) | Turn Pressure (PSI) | Estimated Max Bottom Time (min) |
|---|---|---|---|---|---|---|
| 10 | ||||||
| 15 | ||||||
| 20 | ||||||
| 30 | ||||||
| 40 | ||||||
| 50 | ||||||
| 60 | ||||||
| 70 | ||||||
| 80 | ||||||
| 90 | ||||||
| 100 | ||||||
| 110 | ||||||
| 120 | ||||||
| 130 |
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.
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