Scuba RMV Calculator

Turn the bar per minute you measured on one cylinder into litres per minute, then see what it means on another cylinder and at depth.

Results update as you type.

Quick examples

Load a full example, then change any value.

SAC rate (bar/min)

How many bar the gauge drops per minute, corrected to the surface.

Cylinder size (L)

The cylinder your bar/min figure comes from. An aluminium 80 (AL80) holds 11.1 L.

Quick picks

Compare with another cylinder (L)

Optional. Shows the bar/min to expect on this cylinder. Leave it empty to hide.

Quick picks

Depth (m)

Planned or average depth. Gas use grows with the absolute pressure.

RMV (surface)

Within limits

1.9 bar/min on your 11.1 L cylinder is an RMV of 21.1 L/min. At 18 m you breathe about 59.1 L/min.

SAC on 15 L: 1.41 bar/min
Gas use at 18 m: 59.1 L/min
Gauge drop at 18 m on 11.1 L: 5.32 bar/min
Gauge drop at 18 m on 15 L: 3.94 bar/min

Your RMV on the same scale as our SAC calculator. 15-25 L/min is the typical recreational range.

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These tools are educational planning aids; they are not a substitute for dive training, current printed tables or a dive computer. Verify results against your training and always plan within the limits of your certification.

About SAC and RMV

RMV (respiratory minute volume) is the gas you breathe per minute at the surface, in litres. The cylinder does not change it, so it is the rate to keep in your log and reuse on any cylinder.

On this page SAC means bar per minute at the surface, so it belongs to one cylinder: a bigger cylinder drops fewer bar for the same breath. Our SAC calculator, like many agencies, calls the L/min figure SAC. That is the same number as RMV.

With your numbers

Enter valid values to see the calculation worked through with your numbers.

Formula

RMV from a bar/min rate

RMV = SACbar × V

bar/min on a cylinder

SACbar = (RMV) ÷ (V)

At depth, the same for L/min and bar/min

Xd = X × P

Absolute pressure

P = (d) ÷ (10) + 1

Where

SACbar: gauge drop per minute at the surface (bar/min)
RMV: gas breathed per minute at the surface (L/min)
V: cylinder size (L); twin 12s count as 24 L
X: RMV or SACbar at the surface; d: depth (m)
Only the results are rounded: L/min to 0.1, bar/min to 0.01

How it's calculated

RMV (L/min) = SAC (bar/min) × cylinder size (L).
SAC (bar/min) = RMV (L/min) ÷ cylinder size (L). For another cylinder, the same RMV is divided by that cylinder's size.
Absolute pressure (bar) = depth ÷ 10 + 1.
Gas use at depth = surface value × absolute pressure, for both L/min and bar/min.
L/min values are rounded to 0.1 and bar/min values to 0.01. Only the shown results are rounded; every step uses the unrounded value.

Good to know

Work out your rate from several dives before you plan with it. Cold water, current or a hard swim can raise it a lot on a single dive.
Gas use at depth assumes the whole time is spent at that depth. For a full plan with reserve, use the gas planner.
Like most dive planning, the conversion treats air as an ideal gas. At high fill pressures a cylinder holds slightly less gas than bar × litres suggests.

How to use the RMV calculator

1
Choose SAC to RMV if you know how many bar per minute you use, or RMV to SAC if you know your litres per minute.
2
Enter the cylinder size the rate belongs to. An aluminium 80 is 11.1 L. For twin cylinders add both, so twin 12s are 24 L.
3
Set a depth to see your gas use there. In SAC to RMV, add a second cylinder to see the bar per minute to expect on it.

SAC in bar/min and RMV in L/min

SAC (surface air consumption) in bar/min is how many bar the gauge would drop per minute at the surface. It is tied to the cylinder. For example, 1.9 bar/min on an 11.1 L cylinder is 1.41 bar/min on a 15 L cylinder, because the same breath takes fewer bar from a bigger cylinder.

RMV (respiratory minute volume) is the gas you breathe per minute at the surface, in litres. The cylinder does not change it, so it is the figure to keep in your log and reuse on any cylinder. Many agencies and our SAC calculator call this L/min figure the SAC rate. It is the same number as RMV under another name.

Both values rise with depth. At 18 m the absolute pressure is 2.8 bar, so an RMV of 21.1 L/min becomes about 59.1 L/min and the gauge drops 2.8 times faster than at the surface. The SAC calculator finds your rate from a logged dive, and the gas planner turns it into litres and bar for a planned dive.

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