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Scuba SAC Rate Calculator

Calculate your Surface Air Consumption (SAC) rate from a dive's tank pressure drop, dive time, and average depth.

SAC rate
1.5 bar/min
Ambient pressure at average depth
2.5 ATA
Gas consumed
150 bar
Consumption rate at depth
3.75 bar/min

How it works

Surface Air Consumption (SAC) rate is how much breathing gas you'd use per minute if you were breathing it at the surface (1 atmosphere absolute, or ATA) — the figure that lets you compare gas usage across dives of different depths. It's found by taking the actual per-minute tank-pressure drop during the dive and dividing out the ambient pressure multiplier at the dive's average depth: ATA = depth ÷ 33 + 1 (imperial, feet) or depth ÷ 10 + 1 (metric, meters); consumption per minute = (start pressure − end pressure) ÷ dive time; SAC rate = consumption per minute ÷ ATA. Verified via web search against Divers Alert Network's 'Estimating Your Air Consumption' article and Scuba Diver Life's own SAC-rate explainer.

Normalizing to the surface matters because compressed gas is consumed faster at depth for the exact same breathing pattern — the same number of breaths moves more gas mass, since that gas is denser under higher ambient pressure. A diver breathing at a constant rate uses twice as much tank pressure per minute at 10m/33ft (2 ATA) as they would at the surface, and four times as much at 30m/99ft (4 ATA), even though their actual SAC rate hasn't changed.

FAQ

What's the difference between SAC rate and RMV?

SAC rate is measured in tank pressure per minute (psi/min or bar/min), which is what this calculator reports. RMV (respiratory minute volume) converts that into an actual gas volume per minute (e.g. liters/min or cubic feet/min), which additionally requires knowing your specific tank's water capacity and rated working pressure — a fact that varies by cylinder, so this calculator doesn't assume one. If you know your tank's cylinder factor, you can convert your SAC rate to RMV yourself by multiplying by that tank's own volume-per-pressure-unit rating.

Should I use my actual maximum depth or average depth?

Average depth, not maximum — SAC rate is meant to reflect the ambient pressure you breathed against for the whole dive, and most dives spend time shallower than the maximum depth reached. Many dive computers log average depth directly; if yours doesn't, a rough estimate from your dive profile is more accurate than using the maximum depth for the whole calculation.

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