Guide
What size compressor for an impact wrench
Short bursts, so the tank matters as much as the pump.
Short answer
A 1/2 in impact wrench draws about 4.5 CFM at 90 PSI while the trigger is held, but only in short bursts. A 20 to 30 gallon compressor delivering about 5.1 SCFM or more keeps up with lug nuts and suspension work; a 6 gallon pancake runs it for only about 52 seconds of continuous hammering before the pressure drops.
Average demand versus the burst
An impact wrench is used for a second or two per nut, so averaged over a job it needs little air: about 0.9 CFM at a typical duty cycle, which even a 2.6 SCFM compressor covers. The problem is the stuck nut. Held on the trigger, the wrench draws its full 4.5 CFM, and that has to come from the tank if the pump cannot supply it.
| Compressor | Delivers | Before pressure drops |
|---|---|---|
| 6 gallon pancake | 2.6 SCFM | 52 seconds |
| 30 gallon | 5.1 SCFM | continuous |
When the pressure drops the wrench loses torque quickly, which is exactly when a seized nut needs it most. That is the real reason to buy the larger machine: a 1/2 in wrench rated at 90 PSI will not deliver its rated torque at 70.
Hose and fittings cost more than you think
A long 1/4 in hose with small quick couplers can lose 10 PSI or more at an impact wrench’s flow. Use 3/8 in hose, high-flow couplers, and no more length than you need, or the compressor’s size is wasted before the air reaches the tool.
What about nailers and tire inflators?
A framing nailer uses about 2.2 CFM per second of firing, a fraction of a second per nail, so a pancake compressor handles one comfortably. Tire inflation needs little flow too; any compressor that reaches the tire’s pressure will fill it, just more slowly on a small one.