Tank Autonomy Calculator
Estimate how long your scuba cylinder can last at a planned average depth using your SAC rate and a fixed 50 bar reserve.
How long will your tank last?
Enter your cylinder, pressure, SAC and planned average depth. The calculator estimates usable time before reserve and how long the reserve itself represents at that depth.
How tank autonomy is calculated
Tank autonomy starts with the usable gas in the cylinder: cylinder volume multiplied by the pressure available above the selected reserve. That gas is then divided by your SAC rate adjusted for ambient pressure at the planned average depth.
Example: a 15 L cylinder filled to 200 bar with a 50 bar reserve provides about 2,250 L of usable gas before reserve. At 18 m, a SAC of 20 L/min becomes roughly 56 L/min at depth, giving about 40 minutes of theoretical usable time.
This is an estimate, not a turn-pressure rule. Real consumption changes with current, workload, stress, temperature, buoyancy, equipment and the dive profile. Use a conservative SAC and leave additional gas appropriate to your training and dive plan.
The calculator updates instantly from the values you enter and shows the core planning result in the dark result card.
Use realistic values from your own diving and leave a practical margin for changes in workload, conditions and equipment.
Treat this page as an educational reference and cross-check the result with your training, analysed gas and an appropriate dive-planning method.