SAC Rate

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It's just liters per minute, adjusted for your absolute depth. Hardly worth a spreadsheet.

(liters used / minutes) / average depth in ata

Average depth in ata is (average depth + 10m)/10m
Liters used = size of tank in liters * (starting bar - ending bar)
 
Charlie99:
It's just liters per minute, adjusted for your absolute depth. Hardly worth a spreadsheet.

(liters used / minutes) / average depth in ata

Average depth in ata is (average depth + 10m)/10m
Liters used = size of tank in liters * (starting bar - ending bar)

Charlie, how come your formula doesn't factor in tank's pressure ratings whereas this often quoted site does? If you use two tanks do you just use their total size. i.e. doubles 12L Als would be 24.

By the way, what's a normal SAC rate when using 12L aluminiums (AL80s) doubles?
 
*Floater*:
Charlie, how come your formula doesn't factor in tank's pressure ratings whereas this often quoted site does?
The short answer is that the formula above is for METRIC, the website is for IMPERIAL measurement.

The difference is in how tank sizes are described. The metric standard is to give the internal volume. (Aka water capacity because one way of measuring it is to fill the tank with water, then measure the water as you pour it out.) Internal Volume * pressure in atmospheres gives the 1 ata equivalent volume. 1 atm and 1 bar are just 1% or so different, so for this calculation they are equivalent.

In the imperial method used in the USA, we describe the tank by the total 1 ata equivalent volume. To get the internal volume, one has to divide the rated capacity by the working pressure in atm. Only because of this way tanks are measured does the working pressure come into the equation.

You can use the same formula as in my earlier post with imperial measurements, in that case, the AL80 isn't an 80 cubic foot tank, but is about 0.39 cu ft.

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Normal SAC is anywhere from 0.75cfm / 21lpm for a new diver, to 0.4cfm/11lpm for a calm experienced diver just drifting along with the current. There have been a couple threads and polls on what is average. I usually fall well off to the low side of most dives at 0.4cfm at rest or drift dive, 0.5 when swimming at 1/2kt, and 0.6-0.7 range when working hard against a current.
 
Air intergrated computers will factor in tank pressure since that changes volumn.

No more calculator for me, just push a button :)
 
https://www.shearwater.com/products/swift/

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