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Scuba Surface Air Consumption Calculator

Enter your gas used, dive time and depth to find your SAC rate.

How it is calculated

The tool works in imperial units: pressure drop in psi, time in minutes and average depth in feet. It first finds the absolute pressure at that depth, then divides the real consumption by it to get what you would breathe at the surface:

ATA = depth(ft) ÷ 33 + 1
depth rate = psi used ÷ minutes
SAC = depth rate ÷ ATA

The factor 33 ft per atmosphere is the usual seawater figure. SAC is shown in psi/min, with the ATA and the raw rate at depth beside it. Use the average depth of the dive, not the maximum. All three values must be above zero (a depth of 0 gives no result), and the tool also rejects depths over 1,100 ft, pressure drops over 10,000 psi and times over 5,000 minutes. The figure describes a tank pressure, not a gas volume, so it is only comparable between dives on the same tank size.

Worked example

You used 900 psi from the tank during a 40-minute dive at an average depth of 66 ft. Pressure at 66 ft is 66 ÷ 33 + 1 = 3.00 ATA. Your consumption at depth is 900 ÷ 40 = 22.50 psi/min. Dividing by 3 gives a surface equivalent of 7.50 psi/min. At 33 ft (2 ATA) the same 22.50 psi/min of tank drop would mean a SAC of 11.25 psi/min, so the same drop means a higher breathing rate when the dive is shallower.

Try this example →

Common mistakes

  • Entering depth in metres. The field is in feet, and 20 typed for 20 m is read as 20 ft (1.61 ATA), which makes the SAC much too high.
  • Using the maximum depth for a dive that spent most of its time shallower. SAC should use the average depth over the dive; the maximum overstates the pressure and understates your consumption.
  • Entering the starting pressure instead of the pressure used. The field wants the drop (start minus end), for example 900, not 3000.
  • Comparing psi/min between divers with different tanks. A psi drop is not a volume, so an aluminium 80 and a steel 120 give different numbers for the same breathing rate.
  • Using a single dive that included a stressed ascent or cold water as your planning number. SAC changes with effort, so keep a few relaxed dives to get a realistic value.

Sources

About this calculator

A diver's Surface Air Consumption (SAC) rate measures how much breathing gas they use per minute, normalized to what that consumption would be at the surface — this normalization matters because gas use scales with ambient pressure at depth, so the same diver breathes noticeably more gas per minute at 60 feet than at the surface. Ambient pressure in atmospheres absolute (ATA) is found with ATA = depth ÷ 33 + 1 for saltwater with depth in feet, and dividing actual consumption by that ATA value strips out the depth effect.

This calculator takes the gas used (in psi), dive time (in minutes) and average depth (in feet — not meters) to compute SAC rate in psi per minute. It's a core planning number for certified scuba divers, used to estimate how long a given tank will last on a future dive, plan gas reserves for deeper or longer dives, and track fitness and air-consumption efficiency over time — a skill emphasized in advanced and technical diving training.

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