Scuba Tank Duration Calculator
Calculate scuba tank duration with our free tool. See your stats, compare against averages, and track progress over time.
Reviewed for accuracy by Sher, Sports Science & Nutrition Specialist
Scuba Tank Duration Calculator
Calculator
Adjust values & calculateEnter your values below. Every result is computed in your browser — no data is sent to any server.
Formula: Duration = Usable Volume / (SAC x ATA)
Worked example — Duration: 32 min | Bottom Time: 27 min | Consumption: 2.1 cuft/min
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 Usable pressure = 3000 - 500 = 2500 psi Usable volume = (2500/3000) x 80 = 66.7 cuft Consumption at depth = 0.75 x 2.8 = 2.1 cuft/min Duration = 66.7 / 2.1 = 31.8 minutes Ascent time = 18/9 = 2.0 min Bottom 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 Usable pressure = 3442 - 725 = 2717 psi Usable volume = (2717/3442) x 100 = 78.9 cuft Consumption at depth = 0.6 x 4.0 = 2.4 cuft/min Duration = 78.9 / 2.4 = 32.9 minutes Ascent time = 30/9 = 3.3 min Bottom 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.
What is SAC rate and how do I determine mine?
SAC (Surface Air Consumption) rate is the volume of air you breathe per minute at the surface, measured in cubic feet per minute or liters per minute. To calculate your SAC rate, note your starting and ending tank pressure during a dive at a known depth, record the dive time, and use the formula: SAC = (Pressure Used / Total Tank Pressure x Tank Volume) / (Dive Time x ATA). Average SAC rates for recreational divers range from 0.5 to 1.0 cubic feet per minute, with experienced divers typically consuming 0.4 to 0.6 cuft/min and new divers consuming 0.8 to 1.2 cuft/min. Factors affecting SAC include fitness level, anxiety, water temperature, current, and physical exertion.
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.
What factors increase air consumption during a scuba dive?
Multiple factors can significantly increase air consumption beyond your baseline SAC rate. Physical exertion from swimming against current, carrying heavy equipment, or ascending can double or triple consumption. Cold water increases consumption because the body works harder to maintain core temperature and the denser cold air requires more effort to breathe. Anxiety and stress trigger faster breathing rates, which is why new divers consume much more air than experienced ones. Poor buoyancy control leads to unnecessary swimming and constant adjustments. Breathing through a poorly maintained regulator with high cracking pressure also increases work of breathing and consumption rate.
How do I plan gas for a multi-level dive profile?
Multi-level dive planning requires calculating gas consumption separately for each depth segment and summing the totals. Start by breaking the dive into segments with the deepest portion first. For each segment, calculate the ATA at that depth, multiply by your SAC rate to get consumption at depth, then multiply by the planned time at that depth. Add all segments plus ascent gas and safety stop gas to get total gas required. For example, 10 minutes at 30m (4 ATA x 0.75 SAC = 3.0 cuft/min x 10 = 30 cuft) plus 20 minutes at 15m (2.5 ATA x 0.75 = 1.875 cuft/min x 20 = 37.5 cuft) totals 67.5 cuft plus ascent gas.
What is the difference between SAC and RMV in scuba diving?
SAC (Surface Air Consumption) and RMV (Respiratory Minute Volume) both measure breathing rate but use different units and contexts. SAC is typically expressed in pressure units per minute (psi/min or bar/min) and is specific to a particular tank size. RMV is expressed in volume units per minute (liters/min or cubic feet/min) and is independent of tank size, making it more universally useful for gas planning across different equipment configurations. To convert SAC to RMV, multiply the SAC in psi/min by the tank conversion factor (tank volume in cubic feet divided by working pressure). RMV is preferred for planning because it allows accurate calculations regardless of which tank you will use on the dive.
How does altitude affect scuba tank duration calculations?
Diving at altitude requires adjustments to tank duration calculations because the surface atmospheric pressure is lower than at sea level. At 2000 meters elevation, atmospheric pressure is approximately 0.8 ATA instead of 1.0 ATA. This means the equivalent depth of any given actual depth is greater, and air consumption increases relative to what you would expect at sea level. A dive to 20 meters at altitude is physiologically equivalent to a deeper dive at sea level. Additionally, tanks filled at sea level and transported to altitude will show lower gauge pressure due to the reduced ambient pressure. Divers must use altitude conversion tables or specialized dive computers that automatically adjust for altitude when planning gas consumption.
Can enriched air (Nitrox) extend my tank duration?
Enriched air Nitrox does not directly extend tank duration because the total volume of gas in the tank remains the same regardless of the oxygen percentage. A tank filled to 3000 psi with air and one filled to 3000 psi with EANx32 contain the same total gas volume and will last the same amount of time at any given depth. However, Nitrox indirectly allows longer bottom times because its reduced nitrogen content extends no-decompression limits, meaning you can stay at depth longer before requiring decompression stops. The primary benefit of Nitrox is reduced nitrogen loading and extended no-deco time, not gas supply extension. Divers who hit their NDL limits before running low on gas benefit most from Nitrox.
References
Reviewed for accuracy by Sher, Sports Science & Nutrition Specialist · Editorial policy
Related Calculators
🧮Scuba Weight
Calculate scuba weight with inputs, formulas, and instant results.
🧮Match Duration
Calculate match duration with inputs, formulas, and instant results.
🧮Stretch Duration
Calculate stretch duration with inputs, formulas, and instant results.
🧮Sunlight Duration Planner
Calculate sunlight duration planner with inputs, formulas, and instant results.
🧮Calories Burned Swimming Calculator
Calculate calories burned swimming by stroke type, duration, and body weight.
🧮Cycling Calorie Calculator
Calculate calories burned cycling from power output, duration, and body weight.
🧮Yoga Calorie Calculator — By Style & Duration
Calculate calories burned during yoga by style (vinyasa, hatha, hot, yin) and duration.
🧮Yoga Session Planner Calculator
Plan yoga session structure from warm-up through savasana by focus area and duration.