Calculator Inputs
Formula Used
Ambient pressure: ATA = average depth ÷ depth divisor + 1.
Metric gas used: gas used = pressure drop × cylinder liters × cylinder count.
Imperial tank factor: tank factor = tank cubic feet ÷ service pressure.
Imperial gas used: gas used = pressure drop × tank factor × cylinder count.
Surface air consumption: RMV = gas used ÷ ATA ÷ dive time.
Pressure SAC: pressure SAC = pressure drop ÷ ATA ÷ dive time.
Planned gas need: planned gas = RMV × safety factor × planned ATA × planned time.
Example Data Table
| System | Start | End | Depth | Time | Cylinder | Approx Result |
|---|---|---|---|---|---|---|
| Metric | 200 bar | 70 bar | 18 m | 40 min | 12 L | 13.93 L/min |
| Metric | 210 bar | 90 bar | 24 m | 35 min | 15 L | 15.13 L/min |
| Imperial | 3000 psi | 1200 psi | 60 ft | 45 min | 80 cu ft | 0.43 cu ft/min |
How to Use This Calculator
- Select metric or imperial units.
- Enter starting pressure and ending pressure from the dive.
- Add average depth and bottom time.
- Enter cylinder size, service pressure, and cylinder count.
- Add reserve pressure, target rate, and safety factor.
- Press the calculate button.
- Review SAC, RMV, gas use, and planning values.
- Download the result as CSV or PDF.
Surface Air Consumption Rate Guide
Why SAC Rate Matters
Surface air consumption rate is a normalized breathing value. It estimates how much gas a diver would use at the surface. This makes different dives easier to compare. A deeper dive naturally uses gas faster. SAC removes that depth effect. The result helps divers judge breathing efficiency. It also supports better gas planning.
Understanding the Inputs
The calculator uses starting pressure, ending pressure, average depth, bottom time, and cylinder information. These values describe the gas actually used during a dive. Metric users enter cylinder water volume in liters. Imperial users enter rated tank capacity and service pressure. The tool then converts pressure loss into usable gas volume.
Reading the Result
RMV is the main volume based SAC value. It is shown in liters per minute or cubic feet per minute. Pressure SAC is also shown. That value is useful for repeat dives with the same tank. RMV is better when comparing different tanks. The calculator also shows gas use at depth. This helps explain why deeper dives require larger reserves.
Planning Safer Dives
A single SAC value should not be treated as fixed. Workload, current, cold water, stress, buoyancy, and equipment drag can raise breathing demand. For that reason, this calculator includes a safety factor. It increases the planned gas need. Conservative planning is useful when conditions are uncertain. It is also helpful when diving with a buddy.
Using the Comparison Tools
The target field compares your current RMV against a chosen goal. This may be your personal average. It may also be a training benchmark. A higher value is not always bad. It may reflect difficult conditions or heavy finning. Use repeated results to identify patterns. Better trim, slower movement, and calm breathing often improve gas use.
Frequently Asked Questions
What is surface air consumption rate?
It is a depth-normalized breathing rate. It estimates how much gas a diver uses per minute at surface pressure.
Is SAC the same as RMV?
They are closely related. RMV is volume based, while pressure SAC may depend on tank size and pressure rating.
Why does average depth matter?
Gas density increases with depth. Average depth lets the calculator adjust gas use back to surface pressure.
Should I use metric or imperial units?
Use the system matching your tank markings and pressure gauge. Mixing units can create incorrect gas planning results.
What is a good SAC rate?
A good value depends on training, body size, workload, and conditions. Track your own average over several dives.
Why include a safety factor?
A safety factor adds planning margin for stress, current, cold water, task loading, or unexpected delays during a dive.
Can this replace formal dive planning?
No. It supports calculation practice and planning checks. Always follow training, local rules, tables, and qualified guidance.
Why is my result higher than expected?
High values may come from poor trim, fast swimming, cold water, anxiety, current, leaks, or inaccurate pressure readings.