I see all three ratings given when looking at various compressors. Some give CFM, some give SCFM, and some give ACFM I've been seeing lately. What's the difference between them?

For example, I've found an air compressor I beleive to be half decent. It's one of the nicer 115V compressors (I'm only renting a place right now and am not allowed to put in 230V). Gives a rating of 5.7CFM @ 90psi, and 7.1CFM @ 40psi. Is this enough to run an HVLP spray gun?. My car will have black primer as a top coat.

Anyways, how would these figures compare in SCFM, and ACFM?

Any help would be appreciated....It's been hard finding info on comparing the different ratings.

I don't think that is enough to run HVLP gun. Most HVLP guns run about 13CFM@40psi. Here's a little site to help with the ratings. Closer Look.. I have an Ingersol Rand twin stage 7.5HP 220v hooked to 2 100gallon tanks. It's rated at 25CFM@175PSI, 40CFM@90PSI, 60CFM@40PSI. Before this I used a smaller 110v compressor on a 60 gallon upright tank, rated at 10.7CFM@90 13CFM@40. It worked good but I would always have to stop every so ofter to let it fill back up. When sand blasting I couldn't go more then 30seconds or so at a time, about the same with a DA sander and HVLP gun. What's the problem with a 220v line? The wife won't let you steal the Drier outlet?

ACFM is Actual Cubic Feet per Minute
SCFM is Standard Cubic Feet per Minute. The standard condition is 14.696 psia at 68ºF. To convert from ACFM to SCFM you can use the ideal gas law, we learned in high school, to relate the actual condition specified to the standard condition.

ACFM * (Actual Pressure Specified(psig+14.7))psia/14.7 psia * 528ºR/(Actual Temperature SpecifiedºF + 460)ºR
= SCFM

Although poor practice, CFM is generally used interchangably with ACFM. Some compressors will list ICFM, which is Inlet Cubic Feet per Minute.