Question 1

How long will my scuba tank last?

Accepted Answer

Your tank duration depends on your SAC rate, tank volume, and depth. At the surface, a typical 15L tank at 200 bar provides about 3000 liters of air. At 20 meters (3 ATA), you breathe 3x faster than at surface. A diver with 20 L/min SAC at 20m depth consumes 60 L/min, giving roughly 50 minutes of bottom time.

Question 2

What is a good SAC rate?

Accepted Answer

A "good" SAC rate is between 12-15 L/min (0.4-0.5 cu ft/min) for experienced divers. Beginners typically have 20-25 L/min. Factors affecting SAC include buoyancy control, stress, cold water, and diving fitness. Lower SAC means longer bottom time and safer dives.

Question 3

How do I calculate my turn pressure?

Accepted Answer

Turn pressure (or turn-around pressure) is when you must begin your return to avoid running out of air. A common method is the Rule of Thirds: start with 2/3 for outbound, use 1/3 for return. Alternatively, calculate your Rock Bottom (gas needed for emergency ascent) and subtract from available gas to determine your turn pressure.

Question 4

Why is reserve fixed at 50 bar?

Accepted Answer

For simplicity and safety, this calculator uses a fixed reserve of 50 bar (approximately 725 psi). This represents a conservative emergency gas supply that allows for a controlled ascent, safety stop, and gas sharing with a buddy if needed. More advanced planning should consider your specific dive profile, depth, and SAC rate to calculate an appropriate reserve.

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