Question 1

How long can I scuba dive on a single tank?

Accepted Answer

Your dive duration depends on your personal Surface Air Consumption (SAC) rate, the tank volume, and your depth. As pressure increases with depth, you consume air faster; for example, at 20 meters (3 ATA), you consume air three times faster than at the surface. This calculator computes your exact remaining time by factoring in your reserve pressure (Rock Bottom).

Question 2

What is "Rock Bottom" gas planning?

Accepted Answer

Rock Bottom is the minimum amount of gas required for two divers to ascend safely from the deepest point of the dive while sharing air, including time for a safety stop. It is a critical safety margin calculated based on depth and stress-level air consumption rates, ensuring you never run out of air during an emergency.

Question 3

How do I calculate my turn pressure?

Accepted Answer

Turn pressure is the gauge reading at which you must begin your return to the exit point to ensure a safe ascent. It is calculated by subtracting your required reserve gas (Rock Bottom) from your starting gas, and often splitting the remainder using the "Rule of Thirds" (one third out, one third back, one third reserve).

Question 4

Why does my dive computer show less time than my pressure gauge suggests?

Accepted Answer

Dive computers calculate "No Decompression Limit" (NDL), which is based on nitrogen absorption, not air supply. However, deeper dives are often limited by gas volume (Autonomy) rather than nitrogen. Our Autonomy Computer bridges this gap by calculating exactly how long your gas will last at a specific depth.

Scuba diving autonomy and SAC calculator

FAQs