Guide
What size compressor to paint a car
A spray gun runs continuously, so the compressor has to keep up on its own.
Short answer
A full-size HVLP spray gun uses about 9 CFM without a break, so with the usual 30 percent margin the compressor has to deliver about 11.7 SCFM at 90 PSI: in practice a 14 SCFM machine, which usually means a 60 or 80 gallon, 240 volt compressor. Sanding the car with a dual action sander needs more, about 14.3 SCFM.
Why painting needs a big compressor
Most air tools run in short bursts, so a small compressor and a tank can keep up. A spray gun does not: once a panel is started, the gun runs until the panel is done, and a compressor that falls behind drops the pressure mid-coat. That is when the paint goes on dry, blotchy or orange-peeled. So the compressor has to deliver the gun’s full draw continuously, with a margin, and the tank is a buffer, not the supply.
| Job | Tool draw | Compressor must deliver | Common size |
|---|---|---|---|
| HVLP spray gun | 9 CFM at 40 PSI | 11.7 SCFM | 14 SCFM |
| Dual action sander (prep) | 11 CFM at 90 PSI | 14.3 SCFM | 17.5 SCFM |
What happens with a small compressor
A 20 gallon compressor delivering 4 SCFM, fed from full, keeps a 9 CFM gun going for about 1.1 minutes before it drops to cut-in pressure, then falls further behind every minute. That is enough for a fender, not a door, and nowhere near a whole side. Detail and touch-up guns, which use 4 to 6 CFM, are the realistic option on a small machine.
Read the rating that matters
Compare compressors by SCFM delivered at 90 PSI, not by horsepower, tank size or the headline "CFM" on the box, which is often displacement: a theoretical pump figure 30 percent higher than what comes out of the hose. The SCFM vs CFM page explains how to tell them apart. Add a water separator and a desiccant or refrigerated dryer at the gun: a big compressor makes a lot of water, and water in the line is the other way to ruin a paint job.