Scuba Tank Duration Calculator
Calculate scuba tank duration with our free tool. See your stats, compare against averages, and track progress over time.
Reviewed by Sher, Sports Science & Nutrition Specialist
Formula
Duration = Usable Volume / (SAC x ATA)
Where Usable Volume is the tank capacity multiplied by the usable pressure fraction, SAC is Surface Air Consumption in cubic feet per minute, and ATA (Atmospheres Absolute) equals 1 + depth/10 for saltwater. The result gives dive duration in minutes before reaching reserve pressure.
Worked Examples
Example 1: Standard Recreational Dive
Problem:An AL80 tank (80 cuft) filled to 3000 psi with 500 psi reserve, SAC rate of 0.75 cuft/min at 18 meters depth. How long will the air last?
Solution:ATA at 18m = 1 + 18/10 = 2.8\nUsable pressure = 3000 - 500 = 2500 psi\nUsable volume = (2500/3000) x 80 = 66.7 cuft\nConsumption at depth = 0.75 x 2.8 = 2.1 cuft/min\nDuration = 66.7 / 2.1 = 31.8 minutes\nAscent time = 18/9 = 2.0 min\nBottom time = 31.8 - 2.0 - 3.0 = 26.8 min
Result:Duration: 32 min | Bottom Time: 27 min | Consumption: 2.1 cuft/min
Example 2: Deep Dive with Steel Tank
Problem:A Steel 100 tank (100 cuft) at 3442 psi with 725 psi reserve, SAC 0.6 cuft/min at 30 meters. Calculate air supply time.
Solution:ATA at 30m = 1 + 30/10 = 4.0\nUsable pressure = 3442 - 725 = 2717 psi\nUsable volume = (2717/3442) x 100 = 78.9 cuft\nConsumption at depth = 0.6 x 4.0 = 2.4 cuft/min\nDuration = 78.9 / 2.4 = 32.9 minutes\nAscent time = 30/9 = 3.3 min\nBottom time = 32.9 - 3.3 - 3.0 = 26.6 min
Result:Duration: 33 min | Bottom Time: 27 min | Consumption: 2.4 cuft/min
Frequently Asked Questions
How is scuba tank duration calculated?
Scuba tank duration is calculated by dividing the usable air volume by the air consumption rate at depth. The usable volume equals the tank capacity multiplied by the fraction of pressure above reserve (fill pressure minus reserve pressure divided by fill pressure). The consumption rate at depth equals your Surface Air Consumption (SAC) rate multiplied by the absolute pressure in atmospheres (ATA), which increases by 1 atmosphere for every 10 meters of depth. For example, an 80 cubic foot tank filled to 3000 psi with 500 psi reserve at 20 meters depth with a SAC of 0.75 cuft/min would last approximately 44 minutes.
How does depth affect air consumption and tank duration?
Depth has a dramatic effect on air consumption because the air you breathe must be delivered at the ambient pressure of your depth. At 10 meters (2 ATA), you consume twice as much air as at the surface. At 20 meters (3 ATA), you consume three times as much, and at 30 meters (4 ATA), four times as much. This means a tank that lasts 60 minutes at the surface would last only 30 minutes at 10 meters, 20 minutes at 20 meters, and 15 minutes at 30 meters, assuming constant SAC rate. This exponential relationship between depth and consumption is why deep dives are significantly shorter and why divers must plan gas supply carefully for deeper profiles.
What is the recommended reserve pressure for scuba diving?
The recommended reserve pressure varies by training agency and diving conditions, but the standard minimum is 500 psi (35 bar) for recreational diving. This reserve provides enough air for a controlled ascent from maximum recreational depth (40 meters) including a 3-minute safety stop at 5 meters. Some diving organizations recommend a 50-bar (725 psi) reserve for added safety margin. Technical divers often use the rule of thirds: one-third of gas for the outward journey, one-third for the return, and one-third as reserve. In overhead environments like caves and wrecks, more conservative gas planning with larger reserves is essential because direct ascent to the surface may not be possible.
How do different tank sizes affect dive duration?
Tank size directly determines the total gas volume available. The most common recreational tanks are aluminum 80s (80 cubic feet / 11.1 liters) which are standard at most dive operations worldwide. Steel 100s (100 cubic feet / 14.2 liters) provide 25 percent more gas, extending dive time proportionally. Steel 120s (120 cubic feet / 17 liters) offer 50 percent more gas than an AL80 and are popular among divers with higher air consumption or those doing deeper dives. Smaller tanks like the AL63 (63 cubic feet) are used by divers with low consumption rates or for warm-water shallow diving. Technical divers often use twin tanks or sidemount configurations to carry significantly more gas.
References
Reviewed by Sher, Sports Science & Nutrition Specialist · Editorial policy