What is a normal SAC rate?

Pressure-based SAC depends on the cylinder. Typical recreational RMV reference bands are 15–20 L/min or 0.5–0.7 cu ft/min, but personal trends and dive conditions matter more than the band.

Why does my SAC rate change from dive to dive?

SAC rate varies based on exertion level, water temperature, stress, current, visibility, equipment fit, and even your mood. Cold water, strong currents, and unfamiliar environments all increase air consumption. Track your SAC over many dives to find your average.

Should I use SAC or RMV for gas planning?

Use pressure-based SAC only when the planned cylinder matches the one the rate describes. Use RMV when comparing dives or planning across different cylinder sizes and working pressures. They express the same breathing behavior, but RMV is portable between cylinders.

Diving guide

Understanding SAC Rate: Why It Matters for Every Diver

Learn what Surface Air Consumption rate is, how to calculate it, and tips to improve your breathing efficiency underwater.

Surface Air Consumption (SAC) rate is one of the most important metrics in scuba diving. It tells you how much breathing gas you consume per minute at surface pressure, giving you a depth-independent measure of your gas efficiency. Knowing your SAC rate is essential for gas planning, safety, and becoming a better diver.

What Exactly is SAC Rate?

When you dive deeper, the ambient pressure increases and you consume gas faster. At 10 meters33 feet, the ambient pressure is 2 ATA, so you breathe gas at twice the surface rate. At 20 meters66 feet, three times. SAC rate removes this depth effect by normalizing your consumption back to surface-equivalent values.

This makes SAC rate a consistent personal metric. Whether you dove to 10 m or 30 m33 ft or 100 ft, your SAC rate should be roughly the same (assuming similar conditions and exertion). This consistency is what makes it useful for planning future dives at any depth.

Depth multiplies gas use

For the same breathing pattern, gas consumption scales with ambient pressure. SAC removes that multiplier so dives at different depths can be compared on a surface-equivalent basis.

How to Calculate SAC Rate

To calculate your SAC rate, you need four pieces of information from your dive:

Starting tank pressure — what your gauge read before the dive
Ending tank pressure — what your gauge read after the dive
Average depth — most dive computers record this
Dive time — total time from descent to ascent

The SAC Rate Formula

\text{SAC} = \frac{P_{\text{start}} - P_{\text{end}}}{t \times D_f}

Where $D_f$ is the depth factor that converts actual consumption back to surface pressure:

D_f = \frac{\text{depth (m)}}{10} + 1

D_f = \frac{\text{depth (ft)}}{33} + 1

This gives you SAC in bar/minPSI/min — the rate of pressure drop per minute at the surface.

Worked Example

You dive for 40 minutes at an average depth of 15 meters. Start pressure: 200 bar. End pressure: 80 bar. Tank: 12L.You dive for 40 minutes at an average depth of 50 feet. Start pressure: 3000 PSI. End pressure: 1200 PSI. Tank: AL80.

Depth factor = 15/10 + 1 = 2.5 ATADepth factor = (50 + 33) / 33 = 2.52 ATA

SAC = (200 - 80) / (40 x 2.5) = 120 / 100 = 1.2 bar/minSAC = (3000 - 1200) / (40 x 2.52) = 17.9 PSI/min

That is the pressure-based SAC result. To compare it across cylinder sizes, continue to the linked SAC-versus-RMV guide below.

Try it: SAC Rate Calculator

Start Pressure (bar)

End Pressure (bar)

Avg Depth (m)

Dive Time (min)

Cylinder water volume

SAC: 1.2 bar/min|RMV: 14.4 L/min

Personal rates vary by conditions and dive workload.

Make the measurement worth using

Use average depth, not maximum depth. Maximum depth overstates ambient pressure for a multilevel dive and makes the calculated rate look artificially low.
Measure a representative segment. Either use the full underwater profile consistently or isolate a level segment. Do not include a surface swim or time breathing from the cylinder before descent unless the pressure and time window includes it deliberately.
Respect gauge resolution. A 10 bar or 100 psi reading increment can dominate a short sample. Longer, steady segments and a digital pressure log reduce that rounding error.
Record conditions. Current, cold, workload, suit, cylinder, and stress explain why one number should not become a permanent personal label.

What is a Good SAC Rate?

Pressure SAC cannot be compared without a cylinder. Converted to RMV, broad recreational reference bands are 15–20 L/min for many established divers, 10–15 L/min for experienced relaxed divers, and 20–30 L/min for many newer divers0.5–0.7 cu ft/min for many established divers, 0.35–0.5 cu ft/min for experienced relaxed divers, and 0.7–1.1 cu ft/min for many newer divers. These are descriptive ranges, not performance targets.

A calm, warm, low-current reef dive can produce a much lower SAC than a cold dive in current with task loading, thick exposure protection, or stress. That does not automatically mean one number is "good" and the other is "bad".

How to judge your SAC usefully

Compare SAC against your own dives in similar conditions, not against other divers.
Track trends over time: stability and improved control matter more than a single low number.
Plan gas with conservative assumptions for the hardest part of the dive, not your best-case SAC.
Use SAC as a planning tool and safety metric, not as a scorecard.

Tips to Improve Your SAC Rate

Master your buoyancy. Poor buoyancy leads to constant adjustments, extra finning, and wasted energy. Achieving neutral buoyancy means less effort and lower gas consumption. Practice hovering motionless at a fixed depth.
Breathe continuously and comfortably. Avoid rapid, shallow breathing, but never hold your breath or deliberately restrict ventilation to save gas. Relaxed, adequate breathing supports CO₂ removal; buoyancy, trim, workload, and comfort are safer places to improve consumption.
Streamline your equipment. Dangling hoses, loose accessories, and poor trim create drag. More drag means more effort to move through the water, which means more gas consumed.
Stay calm and relaxed. Anxiety, stress, and excitement all increase breathing rate and gas consumption. Experience and familiarity with your environment naturally reduce stress over time.
Track your progress. Log your SAC rate after every dive. Tracking trends over time helps you understand what conditions affect your consumption and measure your improvement.

Ready to calculate your SAC rate? Use our free SAC Rate Calculator to quickly determine your surface consumption rate from your last dive data. Want to go further and convert your SAC to RMV? Try the SAC Rate & RMV Calculator or read our guide on SAC vs RMV differences.

Sources

Estimating Your Air Consumption · Divers Alert Network
Lessons in Gas Management · Divers Alert Network
NOAA Diving Manual: Diving for Science and Technology (6th ed.) · NOAA — Reference text for diving physics, breathing gases, decompression, and oxygen exposure.

Always use current training materials and operational procedures for dive planning.