Scuba SAC Rate from Dive Log Calculator
Calculate Surface Air Consumption rate from a real dive log.
Enter tank pressure used, depth, and time to get your personal SAC for gas planning.
SAC (Surface Air Consumption) Rate
SAC is the rate at which YOU consume gas at the surface (1 ATA), expressed in cubic feet per minute (cuft/min) or liters per minute (L/min). It’s the foundation of all gas planning.
The formula: SAC = (Pressure used × Tank capacity / Tank rated pressure) / (Dive time × ATA average depth)
Where:
- Pressure used = starting PSI - ending PSI (in psi or bar)
- Tank capacity = volume in cuft or L
- Tank rated pressure = manufacturer’s rated psi (3000, 3442, etc.)
- Dive time = total minutes underwater
- ATA average depth = (depth in feet / 33) + 1 for sw, or (m / 10) + 1
Typical SAC rates:
| Diver Profile | SAC (cuft/min) | SAC (L/min) |
|---|---|---|
| Elite freediver / yoga breather | 0.3-0.5 | 8-15 |
| Excellent / fit recreational | 0.5-0.7 | 15-20 |
| Average male recreational | 0.6-0.8 | 18-23 |
| Average female recreational | 0.5-0.7 | 14-20 |
| New / nervous diver | 0.8-1.0 | 22-28 |
| Stressed / cold / out-of-shape | 1.0-1.4 | 28-40 |
Standard tank capacities:
| Tank Name | Capacity | Rated Pressure |
|---|---|---|
| Aluminum 80 (AL80) | 77.4 cuft | 3000 psi |
| Aluminum 63 | 63 cuft | 3000 psi |
| Aluminum 100 | 100 cuft | 3300 psi |
| Steel HP100 | 100 cuft | 3442 psi |
| Steel HP120 | 120 cuft | 3442 psi |
| Twin AL80 (doubles) | 154.8 cuft | 3000 psi |
Why SAC matters:
- Gas planning: Calculate dive time available at any depth
- Buddy matching: Match dives to lower-SAC diver’s profile
- Trip planning: Pick tanks/gas mix appropriate for your rate
- Tracking improvement: Lower SAC = more relaxed, better breathing
Calculating dive time at depth: Dive time = (Tank cuft × Reserve fraction) / (SAC × ATA at depth)
For 80 cuft tank, 0.7 reserve, SAC 0.6, at 60 ft (3 ATA): (80 × 0.7) / (0.6 × 3) = 56 / 1.8 = 31 minutes of usable bottom time before turnaround
The “rule of thirds”: For non-deco recreational dives:
- 1/3 outbound
- 1/3 return
- 1/3 reserve (don’t touch this)
This is built into the dive-time calculation above with reserve fraction = 0.66 typically.
SAC reduction techniques:
- Slow down: swimming hard at 50% effort uses 4× the gas of slow drifting
- Buoyancy control: any vertical correction wastes gas
- Streamline: every dangling regulator/console adds drag
- Relax: fear/excitement increases breath rate 50%+
- Fitness: improved cardiovascular fitness lowers baseline gas use
- Practice: regular diving alone reduces SAC 20-30% over a season
Cold water effect: Diving in cold water (under 60°F / 15°C) increases SAC 15-30% due to:
- Higher metabolism (shivering, even mild)
- Tighter wetsuit constriction
- Heavier exposure suit drag
Newbie-mistake correction: Many new divers report 0.7+ SAC. After 50 dives, most drop to 0.5-0.6. After 200 dives, 0.4-0.5 is common with good technique.