Gas and SAC rate planner
What your dive will actually cost you in gas, from your own surface air consumption rate.
Free to use, no account needed. The calculator loads below.
Why surface air consumption is the number that matters
Your surface air consumption rate, or SAC, is how much gas you breathe per minute at the surface, measured in litres per minute or cubic feet per minute. It is the one figure that turns a dive plan into a gas plan, because every other consumption number is just your SAC multiplied by the ambient pressure at depth.
At 30 metres you are breathing four times as much gas per minute as you do at the surface. A diver with a 20 litre per minute SAC gets through 80 litres a minute down there. That multiplication is why a dive that felt fine at 18 metres runs you dry at 30.
Working out your own rate
The number is personal and it changes. Fitness, cold, workload, task loading, trim and stress all move it, and a new diver's rate is often double what it will be after fifty dives. Using a textbook average instead of your own is how divers end up short.
To measure it, take a dive at a roughly constant depth, note the pressure used and the time, and convert. The app does this automatically from every logged dive, which is the point: your rate stops being a guess and becomes a running average of how you actually breathe.
Rule of thirds and reserves
The reserve is not the part of the plan you tune when the numbers do not work. For recreational open-water diving, surfacing with 50 bar is the usual floor. For overhead or decompression diving, the rule of thirds is standard: a third in, a third out, a third untouched.
If a planned dive only works by eating the reserve, the dive is too long, too deep, or on the wrong cylinder. Change the plan, not the reserve.
Common questions
What is a good SAC rate for scuba diving?
Most recreational divers sit somewhere between 15 and 25 litres per minute, roughly 0.5 to 0.9 cubic feet per minute. New divers are frequently higher and experienced ones lower, but the useful number is your own, measured across your own dives.
How do I calculate SAC from a dive?
Take the pressure you used, multiply by your cylinder's water capacity in litres to get the volume breathed, divide by the dive time in minutes, then divide by the average ambient pressure in bar. The result is your surface rate.
What is the difference between SAC and RMV?
SAC is often quoted in bar per minute for a specific cylinder, which makes it useless on a different cylinder. Respiratory minute volume is in litres per minute and transfers between cylinders. This planner works in volume for that reason.
How much gas should I plan to surface with?
At least 50 bar for ordinary recreational diving, and a full third of your starting gas for anything overhead or decompression. Plan the reserve first and build the dive inside what is left.
The rest of it lives in the app
The app calculates your SAC from every dive you log and keeps a running personal average, so your gas plans use how you actually breathe rather than a number you guessed once.