Complete Guide to Calculating Your SAC Rate (Calculators!)

How long can I stay in the water for this dive? Do you often wonder this as a scuba diver? Do you just go on autopilot when the guide says, “This dive is supposed to be 60 minutes with an average depth of 20 meters; head to your safety stop at 700 PSI/50 bar”?

While some divers feel like “air hogs” and others seem to use very little air, the easiest and most objective way to plan your dives and predict your gas consumption is with one number. That number is your Surface Air Consumption (SAC) rate.

What is SAC Rate?

SAC rate (Surface Air Consumption rate) is the volume of gas you consume at the surface (1 ATM), per minute. This is different from the volume you use at depth because of Boyle’s Law—we consume a greater volume of gas the deeper we go. Some agencies use RMV (Respiratory Minute Volume), which does not normalize for pressure/depth. I find SAC rate easier because it gives you one consistent number to use for planning, regardless of how deep or shallow you are.

How to Calculate Your SAC Rate

Before the advent of modern air-integrated transmitters, the old-fashioned way to calculate your SAC rate was to manually document your tank pressure, average depth, and time. For the math, it’s much easier to use the metric system.

Here’s the formula:

SAC (L/min) = (Start Pressure – End Pressure) x Tank Volume / (Average Depth in ATA x Dive Time)

Thanks to modern transmitters, this process is now a breeze! For each dive, your AI transmitter already calculates everything except the tank volume, so you can simply multiply that number to get your final SAC rate.

SAC (L/min) = SAC from AI Transmitters (Bar/(ATA*min)) x Tank Volume

>> Read more: “Estimating Your Air Consumption” on Diver Alert Network

SAC Rate Calculator

If you use transmitter, input the transmittor data (bar/min or psi/min) and select the tank you use.

Feel free to comment below or message me to add more types of tanks!

Benefits of Using Your SAC Rate

The danger of tracking this number is that you might get addicted to chasing it and forget to enjoy the dive! However, understanding your baseline SAC rate allows you to do some incredibly useful planning:

• Plan a dive: Once you have your number, you can easily back-calculate how long you can stay at a specific average depth.
• Account for contingency: You can run “what-if” scenarios. What if a current makes you work harder and your SAC rate jumps? You can use a higher, conservative number for your dive plan.
• Track your progress: Tracking your SAC rate over time allows you to see how your gas consumption improves with experience, better buoyancy, and a more relaxed mindset.

Dive Duration Calculator

After observing your SAC rate, you can use this calculator to calculate how long your dive can be.

Or… double your SAC, assuming in an emergency, to see how much time you have left.

Master Your Air: Factors That Impact Your SAC Rate

Your SAC rate isn’t a static number. A variety of factors can influence it, which is why it’s so important to track it across different dives and environments.

• Size/Build: It’s often said that a smaller person uses less air due to smaller lungs. However, a petite person may need to work harder to handle proportionally heavier gear.  In addition, muscle and fat consume gas differently.
• Type of Diving: Physically or mentally demanding dives will naturally consume more gas.
• Environment: Colder water temperatures will cause your body to consume more gas to stay warm.
• State of Mind: When you’re more nervous or in an emergency, your breathing rate will increase, causing your gas consumption to spike.

Over time, my average SAC rate has decreased and converged. Now, my SAC rate for double-tank cold-water dives is approaching what it used to be for single-tank cold-water dives. The more I dive, the better my SAC rate is. Also, I found working out (especially cardio) also seems to help.

Make the Dive Plan Counts!

Mastering your SAC rate is a game-changer. It takes the guesswork out of dive planning and gives you the objective data you need to become a more confident and efficient diver. 

Now that you have the tools, the next step is to get in the water and start tracking.

Let me know in the comments what your SAC rate is, or what factors you’ve noticed affect your air consumption!

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Editorial disclaimer

Please be aware that scuba diving is an inherently risky activity, even with certification and experience. The content on this blog reflects my personal opinions and experiences and should not be considered instructional. Always prioritize safety, seek guidance and certification from qualified diving professionals, and carefully consider the risks involved in any dives.