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Enter your dive data on the left to calculate your SAC rate and RMV.
SAC (Surface Air Consumption) rate is a measure of how much gas a diver uses per minute, expressed as if they were breathing at the surface (1 atmosphere). It is calculated from your dive log data — specifically your start and end cylinder pressures, the depth of your dive, and your bottom time.
Because gas is compressed by depth (you consume more litres of gas per breath at 30 m than at 5 m), SAC normalises consumption back to surface pressure so you can compare dives at different depths. SAC is expressed in bar per minute (metric) or psi per minute (imperial) and is specific to the cylinder used.
SAC rate is one of the most useful numbers a diver can track. It tells you how efficiently you breathe underwater, helps you plan gas requirements before a dive, and lets you measure your improvement over time. As divers gain experience and improve their buoyancy control, SAC rates typically decrease significantly.
RMV (Respiratory Minute Volume) is the actual volume of gas you breathe per minute at the surface, expressed in litres per minute (metric) or cubic feet per minute (imperial). RMV is the tank-independent version of SAC — it represents your true breathing rate as a volume, regardless of which cylinder you used.
Because RMV is expressed as a volume, you can use it to plan dives with any cylinder type. For example, if your RMV is 15 L/min and you plan to dive a 12-litre tank to 20 m (3 ATA saltwater), you will consume approximately 15 × 3 = 45 L/min of compressed gas, so your 12 L cylinder at 200 bar (2,400 free litres) would last around 53 minutes.
RMV is preferred by technical divers and instructors for its universality. Once you know your RMV, you can quickly estimate gas duration for any cylinder at any depth without needing to recalculate from raw pressure figures.
Follow these steps to calculate your SAC rate from your dive log:
For imperial units: SAC = (gas_used_psi ÷ dive_time) ÷ ATA. To get RMV in cu ft/min, multiply SAC by the tank factor (rated volume in cu ft ÷ working pressure in psi).
Use the calculator above to do all of this automatically — just enter your dive data and it computes both SAC and RMV instantly.
RMV (in L/min) is the most standardised way to benchmark your breathing efficiency. Here is how typical divers fall across the range:
| RMV (L/min) | RMV (cu ft/min) | Rating | Typical diver profile |
|---|---|---|---|
| < 12 L/min | < 0.42 cu ft/min | Excellent | Very efficient — experienced, calm, great buoyancy |
| 12 – 16 L/min | 0.42 – 0.57 cu ft/min | Good | Typical experienced recreational diver |
| 16 – 20 L/min | 0.57 – 0.71 cu ft/min | Average | Normal for most recreational divers |
| 20 – 25 L/min | 0.71 – 0.88 cu ft/min | Above Average | Room to improve — work on buoyancy and breathing |
| > 25 L/min | > 0.88 cu ft/min | High | Beginners, stressed divers, high exertion dives |
Keep in mind that SAC and RMV naturally increase during stressful or physically demanding dives — cold water, strong currents, and new environments all elevate breathing rates. The benchmarks above are most meaningful for typical calm recreational dives. Do not be discouraged by a high initial rate; consistent practice almost always leads to significant improvement.
Poor buoyancy is the single biggest contributor to high air consumption. When divers are positively buoyant, they kick harder to stay down, increasing exertion and breathing rate. When negatively buoyant, they work to stay off the bottom. Perfect neutral buoyancy — achieved by fine-tuning weight and BCD inflation — dramatically reduces exertion and allows slow, effortless movement through the water.
Many divers breathe too quickly, taking shallow, frequent breaths. Practice slow, deep, diaphragmatic breathing — inhale fully, pause briefly, exhale slowly and completely. A complete breath cycle of 6–10 seconds dramatically improves gas efficiency compared to rapid shallow breaths. This is especially important in the first few minutes of a dive when many divers are still settling in.
Dangling equipment, a vertical body position, or flailing arms all create drag that requires more effort (and more gas) to overcome. Tuck your gauges and accessories close to your body, maintain a horizontal trim position, and keep your arms still during kicking. Even small improvements in streamlining can meaningfully reduce your SAC rate.
Anxiety and stress spike breathing rate significantly. If you feel uneasy underwater, signal your buddy, stop, and focus on slow breathing before continuing. Building confidence through more dive experience and training in different conditions gradually reduces the ambient stress response that many divers experience.
Like any physical skill, air consumption improves with repetition. Log your SAC rate after every dive using a tool like this calculator. Tracking it over time reveals trends — you will likely see consistent improvement over dozens of dives as your body and mind adapt to the underwater environment.
Plan routes that work with currents rather than against them. Move slowly and deliberately — you are not in a race. Reduce unnecessary swimming and hover in place when observing marine life. The less physical effort required, the lower your gas consumption.
Use these tools alongside your SAC rate for complete gas planning: