How to figure your SAC.

[spectrum]

Thanks Pete and Andy. I think I will spend a little more time in the pool and condition a little more. See if that brings down my numbers a bit. My wife's SAC must be around .35 or so. She thinks I'm an air hog!

Ron Shephard

If you can do pool time spend some of it doing laps with your snorkel. Overcoming the dead air space will develop a long deep breathing style that will serve you well.

Pete

 

[Charlie99]

Okay, I just tried computing my SAC rate for my last dive. If my numbers are correct and I did everything right my SAC rate came out at .52. Is this a good number or a bad number?

It's best to avoid thinking of SAC numbers as good or bad. Your SAC is what it is. While over the long term, it will change, when you plan a dive, it's important to use real numbers rather than wishful thinking.

Spectrum's and H2Andy's answers are pretty much in line with my observations. If an instabuddy doesn't know his SAC, I just assume 0.75cfm for planning purposes, and that is usually pretty close.

 

[Willie]

Here is the formula the way I use it on a spreadsheet.

(((Tank Volume ÷ Tank Psi Rating) x Psi Used) ÷ Actual Dive Time) ÷ Average ATA = SAC
​

I am attaching the spreadsheet in xls format, but I dont have Excel so I cant guarantee it works. I use it on Linux in Open Document Spreadsheet format.

Feel free to comment or critique. My wife reminds me regularly that I am not always right.

Willie

 

[Dark Wolf]

Thank you all for your posts. The posts make much more sense than what the book says.

Thanks again.

Dark Wolf

 

[TSandM]

Just one more comment, that SAC rate is not a number, it's a range. It's very strongly affected by what you are doing during a dive. Swimming into current, or working on new skills can drive it up. My husband burned a bunch of gas today helping catch a new diver with some buoyancy problems who was headed for the surface. I average around .4, but a night dive running line was .7.

So take a bunch of measurements over different dives and get a sense for how you do under various circumstances, and you'll have a much more useful set of numbers for doing dive planning.