Air Time Calculator
How long will your tank last at depth? Enter your current pressure, depth, and SAC rate to calculate remaining air time and plan your gas management before and during a dive.
Tank & Dive Parameters
Minimum pressure to surface with. Typically 50 bar.
Results
| Depth | Minutes |
|---|---|
| 5m | 53 |
| 10m | 40 |
| 15m | 32 |
| 20m * | 26 |
| 30m | 20 |
| 40m | 16 |
* current depth
What is Air Time?
Air time (or bottom time) refers to how long your breathing gas will last at a given depth. Because pressure increases with depth, your regulator delivers gas at the same pressure as your surroundings - meaning each breath contains more gas molecules at depth than at the surface. A tank that lasts 60 minutes at the surface will last roughly 30 minutes at 10m and only 20 minutes at 20m.
The key variable is your Surface Air Consumption (SAC) rate - the litres of gas you consume per minute at the surface equivalent. Multiply your SAC rate by the ambient pressure (depth in bar + 1) to get your actual consumption rate at any depth.
The Rule of Thirds
For overhead environments (caves, wrecks, ice diving), the standard gas planning rule is thirds: use one third of your gas going in, one third coming out, and keep one third in reserve for emergencies. This means you turn around when you reach 2/3 of your starting pressure.
For open water recreational diving, the common approach is to plan a 50 bar reserve and begin your ascent when your SPG reads that level. Some agencies recommend a higher reserve of 70-80 bar for newer divers or challenging conditions.
Factors that Affect Air Time
Several variables can significantly increase your gas consumption:
- Exertion: Swimming hard against a current can triple your SAC rate.
- Cold water: Your body works harder to stay warm, burning more gas.
- Stress or anxiety: Elevated breathing rate increases consumption by 50-100%.
- Depth: Gas consumption scales linearly with absolute pressure.
- Equipment fit: A poorly fitted mask or wetsuit increases discomfort and breathing rate.
- Experience level: Novice divers typically breathe 20-30 L/min; experienced divers often manage 10-14 L/min.
Planning Your Gas
Always plan for a worst-case SAC rate, not your best. If you normally breathe 14 L/min in calm conditions, plan using 18-20 L/min to account for any unexpected current, exertion, or stress. Gas planning should be conservative - running low on gas is one of the leading causes of dive accidents.
Before any dive, agree a turn pressure with your buddy so you both surface with a comfortable reserve. Never accept a plan that requires perfect conditions to complete safely.