SAC Rate Calculator: Measure and Plan Your Gas Consumption
1. Measure your SAC rate
From a real dive: the gas you used, the time and the average depth.
Your SAC rate: 0.52 cu ft/min
- SAC rate
- 0.52 cu ft/min
- In liters
- 14.7 L/min
- In this cylinder
- 20.1 psi/minat the surface
The work
- Gas used3,000 − 1,000 = 2,000 psi, or 2,000 ÷ 100 × 2.58 = 51.6 cu ft
- Per minute at depth51.6 cu ft ÷ 45 min = 1.15 cu ft/min
- Average ATA40 ft ÷ 33 + 1 = 2.21 ATA
- SAC rate1.15 ÷ 2.21 = 0.52 cu ft/min
One dive is one data point. Measure several and average them. Psi per minute only applies to this cylinder; cubic feet per minute works with any.
2. Plan with it
How fast your gauge will move at depth, and how long your gas lasts.
57 psi a minute at 60 ft
- Gas per minute
- 1.47 cu ft
- On your gauge
- 57 psi/min
- 1,100 psi lasts
- 19 min
The work
- ATA60 ft ÷ 33 + 1 = 2.82 ATA
- Gas per minute at depth0.52 cu ft/min × 2.82 ATA = 1.47 cu ft/min
- Pressure per minute1.47 ÷ 2.58 × 100 = 57 psi/min
- How long it lasts1,100 psi ÷ 57 psi/min = 19.4 min
For planning, UTD uses 0.5 cubic feet a minute at rest, 0.75 while swimming and 1.0 under stress. Plan reserves with the stressed rate, whatever your measured rate says.
A training aid, not a substitute for training or your team’s plan. Imperial units, salt water.
How do you calculate your SAC rate?
Three steps. Turn the pressure you used into cubic feet with your tank factor. Divide by the dive time. Then divide by your average depth in atmospheres, which is depth ÷ 33 + 1.
Say you used 2,000 psi from an AL80 over 45 minutes at an average of 40 feet. That’s 20 × 2.58 = 51.6 cubic feet, or 1.15 a minute at depth. At 2.21 ATA, your SAC rate is 1.15 ÷ 2.21 = 0.52 cubic feet a minute.
How do you plan with it?
Run it the other way. Breathing rate × ATA gives the gas you use per minute at depth. Divide by your tank factor and multiply by 100, and you know how fast your gauge will move. That’s the number to have in your head before you look at the gauge.
Measure it. Don’t guess it.
One dive is one data point. Log your start and end pressure, time and average depth on every dive, run the numbers and average them. Your rate changes with cold, workload, current and stress, so plan reserves with the stressed rate, never your best day. For more, read How to Calculate Your SAC Rate and RMV and how to improve your air consumption.
Frequently asked questions
What is a SAC rate?
Your surface air consumption rate: the gas you’d breathe per minute at the surface. In cubic feet per minute, it works with any cylinder and lets you predict your gas use at any depth.
What’s a good SAC rate?
It varies with the diver, the dive and the conditions. For planning, UTD uses 0.5 cubic feet per minute at rest, 0.75 while swimming and 1.0 under stress. Your own measured rate tells you more than any target.
Why use average depth instead of maximum depth?
Because you breathe at every depth you visit. Your computer’s average depth gives a truer rate. Maximum depth makes your rate look better than it is.
What’s the difference between SAC and RMV?
Both describe gas used per minute at the surface. SAC is often given in psi per minute, which applies to one cylinder. RMV is in cubic feet or liters per minute and works with any cylinder. This calculator gives both.
Related reading
How to Calculate Your SAC Rate and RMV
How to calculate your surface consumption rate from your logbook, convert between psi and cubic feet, and use it to plan gas at depth, with worked examples.
Read articleHow to Improve Air Consumption
Air consumption improves when the whole system does: correct weight, horizontal trim, efficient kicks and calm breathing. What works and how to measure it.
Read articleInstruments Should Confirm What You Already Know: Gas Math Underwater
Why UTD divers run their gas, time and depth numbers in their heads during the dive, how to do the math, and what to do when the gauge disagrees.
Read article