SAC Rate Calculator
Your Surface Air Consumption (SAC) rate tells you how efficiently you breathe underwater. Tracking it over time is one of the best ways to measure your progress as a diver.
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What is SAC Rate?
Surface Air Consumption (SAC) rate, also known as Respiratory Minute Volume (RMV), measures how much breathing gas you consume per minute normalised to surface pressure. It's the single most important number for dive planning because it lets you predict gas usage at any depth.
How is SAC Rate Calculated?
The formula accounts for the increased gas density at depth:
- Gas consumed = (start pressure - end pressure) x tank volume in litres
- Consumption at depth = gas consumed / dive time
- SAC rate = consumption at depth / ambient pressure (depth/10 + 1)
For example, using 150 bar from a 12L tank over 45 minutes at an average of 18m: gas consumed = 1,800L, rate at depth = 40 L/min, ambient pressure = 2.8 bar, SAC = 40 / 2.8 = 14.3 L/min.
Typical SAC Rates
New divers commonly have SAC rates of 18-25 L/min. With experience and improved buoyancy control, most divers can reduce this to 12-16 L/min. Experienced technical divers often achieve rates below 12 L/min. Factors that increase SAC rate include cold water, strong currents, exertion, stress, and poor trim.
How to Improve Your SAC Rate
- Perfect your buoyancy - constant small adjustments waste gas
- Slow down - swim at half the speed you think is right
- Streamline your gear - dangling equipment creates drag
- Breathe deeply and slowly - avoid shallow, rapid breathing
- Relax - anxiety is the biggest gas waster of all