Diving tool · Air
SAC rate calculator: air consumption and tank duration
First measure your consumption from a dive, then use it to see how long your tank will last on the next one. Consumption is rounded up, duration down.
1 · Measure from your dive
Surface air consumption (SAC)
1.5 bar/min
Respiratory minute volume (RMV)
18 L/min
Exact result 1.48 bar/min; both rounded up. The RMV has been copied into the plan below.
2 · Plan your next dive
Enter a reserve pressure to see the air time.
Estimated air time
Consumption at this depth
This does not replace your dive computer or your training.
Reading the result
- The result is the average of one past dive. Stress, cold, current and workload can multiply consumption: the US Navy gives 6–10 L/min at rest and over 100 L/min during hard work.
- The planned time is not bottom time; it is the whole dive from descent to surfacing.
- The gas needed to bring an out-of-air buddy to the surface with you belongs inside your reserve (DAN Europe).
- The calculation is for seawater and a single tank; depths beyond 40 m are not calculated.
How much reserve?
Primary sources give no single number for everyone. DAN Europe’s approach: at every point of the dive you need enough gas to reach the surface safely with an out-of-air buddy, and that depends on depth, consumption and tank.
DAN Europe’s example: at 30 m with 15 L/min, this minimum is about 550 litres (about 50 bar in an 11-litre aluminium tank); the author adds a 50–100% safety margin and suggests 80–100 bar.
The rule of thirds (a third out, a third back, a third in reserve) is for overhead environments such as caves and wreck penetration, where you cannot ascend directly; it is not part of this open-water calculation.
How the calculation works
The chain from the US Navy Diving Manual and the NOAA formula book: surface consumption from the pressure drop, converted to litres with the tank volume, consumption at depth, and usable air divided by that consumption. P pressure (bar), t time (min), D depth (m), V tank volume (L).
| Value | Formula (metric, seawater) | Rounding |
|---|---|---|
| SAC | (P₁ − P₂) ÷ t ÷ (D ÷ 10 + 1) | Up (conservative) |
| RMV | SAC × V | Up (conservative) |
| Consumption at this depth | RMV × (D ÷ 10 + 1) | Up (conservative) |
| Estimated air time | (Pdolum − Pyedek) × V ÷ CD | Down (conservative) |
Average depth is used; using maximum depth would make consumption look lower than it was.
In imperial units depth is converted to ata with D ÷ 33 + 1 (fsw), and the tank constant k = rated volume ÷ rated pressure replaces tank volume (NOAA). SAC in psi/min is rounded up to a whole number, RMV and consumption at depth in ft³/min up to two decimals.
Sources
- US Navy Diving Manual, Rev. 7 — §7-5.1 Duration of Air Supply (formula and worked example)
- NOAA Diving Program — Diving Medical Technician Reference and Formulas (air requirement formulas)
- DAN Alert Diver — Estimating Your Air Consumption (Mike Ange, 2010)
- DAN Europe — Let’s Talk About Gas Planning (Tim Blömeke, 2022)
- SDI/TDI — Air Management and the Importance of Learning SAC (2012)