It's more air capacity. I had a 15 gallon tank, but a 16.x cfm at 90 psi. The sand blaster said I needed minimum of 11. It worked, somewhat. I'd get bout 90 seconds worth of blasting before it'd surge. As the motor kicks on, it pulses the air flow.
Ended up buying an 80 gallon last year, 500 bucks but I can now do almost an entire fender inside and out before the motor kicks on