Sizing
What size air compressor for a full auto shop
For a full auto shop (impact, ratchet, die grinder, sander, cut-off tool and blow gun together) plan on 19.3 CFM at 90 PSI after a 30 percent margin: an 80 gallon or larger, 240V, 5 HP compressor. That means a 35 A, 240V circuit with 8 AWG copper for a motor in the 3 to 5 HP class.
The air budget for this work
| Tool | CFM | Duty | Average CFM |
|---|---|---|---|
| 1/2 in impact wrench | 4 | 25 percent | 1.0 |
| 3/8 in air ratchet | 3 | 25 percent | 0.8 |
| Die grinder | 4 | 100 percent | 4.0 |
| Dual-action sander | 6 | 100 percent | 6.0 |
| Cut-off tool | 5 | 50 percent | 2.5 |
| Blow gun | 2.5 | 25 percent | 0.6 |
Average draw is 14.9 CFM and peak is 24.5 CFM. Because one of these tools runs continuously (6 CFM), the requirement is set by that tool rather than by the average, then increased 30 percent for wear and cold-day losses. The figures are typical published values: use the CFM printed on your own tool, and compare it with the compressor's CFM at 90 PSI, never its peak horsepower or tank size.
This is too much air for a 15 A household circuit, so the compressor wants 240V and a circuit your electrician confirms before you buy. Quiet, oil-free models are worth their price in an attached garage.
Shop for this size
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Amazon and Grizzly, side by side
Each card shows an Amazon pick and a Grizzly Industrial pick for the same job.
20-gallon quiet compressor
Both are oil-free, quiet-series 20-gallon compressors, so they are tolerable in an attached garage. Pick on the sale, the warranty path and the noise rating you can live with.
Prices change often and Grizzly runs sales, so the buttons show current prices.
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Frequently asked questions
Is a 6 gallon pancake compressor enough for a full auto shop?
A 6 gallon pancake compressor delivers a few CFM at 90 PSI. For a full auto shop the requirement here is 19.3 CFM, so a pancake unit is undersized.
This page is researched guidance, not professional electrical, engineering or safety advice. Circuits, loads and clearances depend on your house, your service and your town: have a licensed electrician confirm any wiring, and check local code and each manufacturer's manual before you act.
