Surface Air Consumption (SAC) Calculator
Calculate your gas consumption rate for safer dive planning.
Imperial (Feet/PSI)
Metric (Meters/Bar)
Atmospheres Absolute (ATA):
0
SAC Rate (PSI/min):
0
RMV (CuFt/min):
0
*RMV (Respiratory Minute Volume) is the volume of gas you breathe normalized to surface pressure.
Understanding Surface Air Consumption (SAC)
For Scuba divers, knowing your SAC rate is a fundamental skill for dive safety and planning. Your SAC rate measures how much air you consume at the surface. Since air compresses as you go deeper, your actual consumption rate increases with depth. By normalizing your consumption to surface levels, you can accurately predict how long a tank will last on future dives at different depths.
Why Calculate Your SAC Rate?
- Gas Planning: Determine if you have enough gas to complete a specific dive profile and required safety stops.
- Track Progress: Monitor how your air consumption improves as your buoyancy and relaxation techniques get better.
- Identify Issues: A sudden spike in SAC rate can indicate stress, overexertion, or equipment problems.
- Buddy Comparison: Help plan dives around the diver with the highest consumption rate to ensure everyone returns with a safe reserve.
The Formula Behind the Math
The calculator uses the following physics-based formulas:
1. Pressure at Depth (ATA):
Imperial: ATA = (Depth / 33) + 1
Metric: ATA = (Depth / 10) + 1
2. SAC Rate (Pressure/min):
SAC = ((Start Pressure - End Pressure) / Time) / ATA
3. RMV (Volume/min):
RMV = SAC * (Tank Volume / Working Pressure)
Realistic Example
Imagine a diver using a standard Aluminum 80 (80 cubic feet, 3000 PSI) for a 40-minute dive at an average depth of 66 feet (3 ATA). They start with 3000 PSI and end with 1000 PSI.
- Pressure used: 2000 PSI
- Consumption at depth: 2000 PSI / 40 min = 50 PSI per minute.
- SAC Rate: 50 PSI / 3 ATA = 16.6 PSI per minute.
- RMV: 16.6 * (80 / 3000) = 0.44 Cubic Feet per minute.
An RMV of 0.4 to 0.5 cu ft/min is typical for an experienced, relaxed diver in calm conditions. Beginners often see rates of 0.7 to 1.0 cu ft/min.