SAC Rate Calculator

Updated November 2026 · free, works in your browser

Your SAC rate (surface air consumption) is the amount of gas you breathe each minute, converted to what it would be at the surface. Enter your tank size, the pressure you used, your dive time and your average depth, and the calculator gives you your RMV in litres or cubic feet per minute, plus the pressure-based SAC in bar or psi per minute.

How to use the SAC rate calculator

1. Choose metric (bar, litres, metres) or imperial (psi, cubic feet, feet).
2. Enter the tank size. In metric this is the water volume in litres, for example 12. In imperial it is the rated capacity in cubic feet, for example 80, together with the rated pressure of the tank in psi.
3. Enter the pressure used: starting pressure minus ending pressure.
4. Enter the dive time in minutes and your average depth, taken from your computer or log.
5. Read the RMV, the SAC pressure rate, the total gas used and the average ambient pressure. The numbers update as you type.

How it is calculated

The calculation uses the usual relationship between depth, pressure and gas volume, with gas treated as ideal.

• Ambient pressure in ata = depth ÷ 10 + 1 with depth in metres, or depth ÷ 33 + 1 with depth in feet. This approximates sea water.
• Gas used = pressure used × tank volume in litres (metric). In imperial, gas used = pressure used ÷ rated pressure × tank capacity in cubic feet.
• RMV (respiratory minute volume) = gas used ÷ dive time ÷ ambient pressure.
• SAC (pressure based) = pressure used ÷ dive time ÷ ambient pressure.

The pressure-based SAC only describes the tank you used, so it changes with tank size. The RMV is a volume and can be applied to any cylinder, which is why it is the better figure for gas planning. The method follows the standard approach in dive training texts. The calculator ignores gas compressibility at high pressures and uses a simple average depth, so treat the result as an estimate.

Ambient pressure at common depths

Frequently asked questions

What is the difference between SAC and RMV?

SAC is usually expressed as pressure per minute, such as bar or psi, and depends on the tank you used. RMV is expressed as a volume per minute, such as litres or cubic feet, and does not depend on the tank.

Which depth should I enter?

Use the average depth of the dive from your dive computer. For a more accurate figure, calculate from a section of the dive at a steady depth.

Why is my SAC higher on some dives?

Cold water, hard finning, current, task loading, a new or heavy drysuit, nervousness and poor trim can all raise gas use. Your figure will vary from dive to dive, so averaging several dives gives a more useful number.

Should I plan with my relaxed rate?

Many divers plan with a higher figure than their relaxed rate, because stress or an emergency can raise consumption sharply. Follow the gas planning rules from your training agency and use appropriate reserves.

Does the calculator work for nitrox or other gases?

Yes. The consumption is a volume of whatever gas is in the tank, so the calculation is the same. Mixes and decompression gases need their own planning.

Planning dives away from home

Once you know your RMV, you can estimate how long a tank lasts at the depth of a wreck or reef before you book the boat. If you are choosing a dive destination, check the usual depths, the number of dives per day and the cylinder sizes on offer, then pick accommodation close to the dive base or harbour so early departures and surface intervals stay relaxed.