How is scuba tank duration calculated?

Tank duration is calculated by dividing your total available air volume (Tank Volume × PSI) by your consumption rate at depth. Because pressure increases with depth, you consume air much faster as you go deeper.

What is SAC rate (Surface Air Consumption)?

SAC rate is the amount of air a diver breathes at the surface. For recreational divers, an average SAC rate is between 15 and 25 liters per minute (roughly 0.5 to 0.75 cubic feet per minute).

Does tank size affect bottom time?

Yes. Larger tanks, such as an Aluminum 100 or Steel 120, hold more air and thus provide longer bottom time than a standard Aluminum 80, assuming all other factors remain constant.

How much faster do you breathe at 30 meters?

At 30 meters (4 ATA), you breathe exactly four times as much air per breath as you do at the surface. A tank that lasts 60 minutes at the surface would only last 15 minutes at 30 meters.

Dive Planning & Safety

Scuba Tank Duration Converter

Predict your bottom time. Calculate precisely how long your air will last based on depth, breathing rate, and tank capacity.

Pre-Dive Variables

Planned Depth

SAC Rate

L/min

Tank Selection

Start Pressure BAR

Reserve (Turn) BAR

Estimated Bottom Time

Safe Bottom Time

27 min

Excludes ascent & deco time.

Consumption at Depth

60.0 L/min

Available Air

1,665 Liters

Factors Affecting Gas Duration

Thermal Regulation

If a diver is cold, their body consumes more oxygen to generate heat, significantly increasing their breathing rate. Proper wetsuit/drysuit selection is essential for maximizing bottom time.

Stress and Exertion

Panic or high levels of physical activity (like swimming against a strong current) can quadruple a diver's SAC rate in seconds, leading to unexpectedly rapid air loss.

Safety Note

⚠️ EXTREMELY IMPORTANT:

This calculator provides theoretical estimates only. Always monitor your actual pressure gauge (SPG) continuously during a dive. These calculations do not include the air required for your ascent, possible deco stops, or emergency procedures. Never dive to the absolute limit of your calculated duration.