The Best SAC Rate Calculator

Calculating your real SAC rate

In technical diving, gas planning is critical. Unlike recreational dives, most technical dives don’t allow direct access to the surface. If anything goes sideways during the dive, you must deal with it on the bottom.

Your best asset when dealing with problems is time, which means having sufficient gas available to keep breathing long enough to solve the problem. SAC stands for “Surface Air Consumption.” It applied to all scuba diving breathing gasses, not just air. Sometimes, you’ll see the term, RMV (Respiratory Minute Volume) used to mean the same thing. They’re not the same thing, but close enough that either is fine.

Your SAC Rate is the rate in cubic feet (for this SAC calculator anyway) that you consume a given breathing gas. It is adjusted to the volume of gas you’d consume at the surface. That way, the calculation is useful for dives to any depth.

I’ll get into details later, or in some future article.

This is the best SAC rate calculator on the Internet. I wrote it as a plugin, which I think is pretty cool. What’s different about this SAC Calculator is I have accounted for any gas you use to inflate your drysuit, and/or the gas you use in your BCD or wing.

I also account for altitude, fresh vs. salt water and some other factors. Check it out!

SAC Rate Calculator

Dive

Avg depth (ft) Dive time (min)

Max depth (ft) (optional) Time at max depth (min) (optional)

Elevation (ft) Water

Cold water (< 50°F)

Tank

Rated volume (cu ft) Rated pressure (psi)

Start pressure (psi) End pressure (psi)

Extras

Optional estimates. If you don’t use a wing or drysuit, leave them off.

I inflated my wing

Wing lift (lb) Wing fill level

Times inflated

I used a drysuit

Drysuit size Override suit gas used (cu ft @ 1 atm)

Calculating SAC the “Usual” Way

It is common to calculate SAC rate by conducting a series of “SAC swims.” A SAC swim is a timed event where the diver swims at a specific depth for a specified time, noting tank pressure before and after the swim. Using this information and a “SAC rate formula” you can calculate your surface air consumption.

The problem is we treat this number as truth and plan all future dives as though gas consumption will match that 5 minute swim.

This SAC calculator attempts to determine your realistic gas requirement by averaging your entire dive and factoring in variables like drysuit and BCD inflation.

There bugs, no doubt, so check this against other methods if you plan to use it for real dives.

Also, I have only accounted for single tank diving so far. Later, I’ll do the programming to include doubles and sidemount diving. I’m also working on a cool way to account for gas switches and gas consumption during deco stops.

For now, this is all there is. Stay tuned…