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SAC calculator

SAC & RMV calculator

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Your surface air consumption is the one number that turns “I use a lot of air” into something you can actually plan with. Take the figures off one dive — ideally a calm section at a steady depth — and this works out what you breathe per minute at the surface, which is the figure gas planning is built on.

What the calculator does

It follows the method DAN publishes: work out the gas you used, divide it by the time, then divide by the ambient pressure to bring it back to a surface-equivalent figure.

SAC (L/min) = (start bar − end bar) × cylinder litres ÷ minutes ÷ ((depth ÷ 10) + 1)

DAN describes the same five-step process in pressure terms and then multiplies by cylinder water capacity to reach RMV, with a worked example arriving at 22 litres per minute from an 11 L cylinder, and a metric-to-imperial cylinder factor of 80 ÷ 3000 = 0.0267 cu ft per psi DAN — Estimating Your Air Consumption. Dive Training sets out the same idea as a surface test and a depth test, noting that at 33 ft you consume twice the surface rate and at 66 ft three times Dive Training — Air Consumption Essentials.

Swipe the diagram sideways to see it full size

Depth is doing this, not your lungs. One diver, breathing exactly the same way, at four depths. The regulator delivers gas at ambient pressure, so the same breath empties four times as much cylinder at 30 m as it does at the surface. This is why a personal SAC figure is only useful once you divide the depth back out of it — and why your air seems to vanish on the deep dive even though nothing about you changed.

Depth model. The calculator uses 10 metres of seawater per bar. In fresh water the ambient pressure at a given depth is slightly lower, so a lake dive will read a little conservative here.

What counts as a normal figure

No certifying agency publishes an expected SAC range for divers with 0–50 dives. We looked. Agencies publish methods, planning conventions and workload tables — not certification-level benchmarks. Any tool that tells you “a new diver should be at X L/min” has made that number up. These are the figures that are actually published:

Published reference	Value	Source
Human at rest at the surface	≈6 L/min	CMAS Europe
Baseline for a relatively experienced diver	14–16 L/min	TDI/SDI
Surface, light to moderate work	20 L/min	DAN Smart Guide
Value adopted for dive planning	25 L/min	CMAS Europe
Surface, vigorous work	70 L/min	DAN Smart Guide
Aluminium 80 duration at 100 ft, light to moderate work	17 min	DAN Smart Guide
Typical SAC for divers with 0–50 dives	not published	—

The useful comparison is you against yourself, in comparable conditions, over several dives. A single dive with a current in it tells you almost nothing.

How to get a figure worth having

Pick a calm section of the dive at a steady depth. Note the depth, the time and your pressure at the start.
Swim at an unhurried pace with neutral buoyancy and horizontal trim. Do not change your breathing because you are measuring it.
Note the pressure and time at the end of the section, and the average depth from your computer.
Enter the four figures here. Repeat over three or four dives before you treat the average as yours.

You have done it whenYou have three comparable dives and the numbers land within a few litres per minute of each other.

Safety

Breathe continuously. Never hold your breath or skip-breathe to bring this number down — that risks lung overexpansion injury and carbon dioxide retention.
This is a planning aid, not a gas supply. Always dive the reserve and turn pressures agreed with your buddy or divemaster, whatever the calculator says.
A calculated figure from a calm dive will underestimate what you need in current, cold or a task-loaded situation. Plan with a margin.

Sources