Every pneumatic tool we ship — from a die grinder to a twin-hammer impact wrench — has an air demand stamped on the plate. Get this step right and your whole line runs at full power; get it wrong and tools bog down the moment two of them fire together. Here is the field method we give distributors.
What CFM and SCFM actually mean
You will see two numbers: CFM (cubic feet per minute) and SCFM (standard CFM, corrected to a reference pressure and temperature). Always size from SCFM at your working pressure (typically 90 psi). A tool rated 4 SCFM @ 90 psi needs 4 cubic feet of free air per minute delivered at 90 psi — not at the compressor's unloaded rating.
Step 1 — read every tool plate
List each air tool with its SCFM @ 90 psi. Typical workshop values (your tool may differ — read the plate):
- Die grinder: 4–6 SCFM
- 1/2" impact wrench: 4–5 SCFM
- Air drill: 3–4 SCFM
- Needle scaler: 6–8 SCFM
- Spray / airbrush: 0.5–2 SCFM (airbrush), higher for spray guns
Step 2 — apply duty cycle
No tool consumes air 100% of the time. A grinder cutting intermittently might be at 50% duty; an impact wrench snapping bolts might be 30%. Multiply each tool's SCFM by its duty cycle to get its average demand.
| Tool | SCFM @90psi | Duty cycle | Average demand |
|---|---|---|---|
| Die grinder | 5 | 50% | 2.5 |
| Impact wrench | 4.5 | 30% | 1.35 |
| Air drill | 3.5 | 40% | 1.4 |
| Total average | — | — | 5.25 |
Step 3 — size the compressor and add margin
Take the total average demand (5.25 SCFM above) and add 25–30%. Target a compressor free-air delivery of about 6.5–7 SCFM @ 90 psi. Buy the delivery, not the tank — a big tank on an undersized pump still starves.
Step 4 — size the receiver tank for the peaks
The receiver smooths short bursts when two tools fire at once. A larger tank (e.g., 20–30 L for a small shop, bigger for production) buys time between compressor cycles. It does not replace inadequate pump delivery, but it stops momentary pressure drops.
Don't forget the air line
Undersized hose and a restrictive coupler quietly rob you of pressure. Use adequate hose ID, keep runs short, and pair the right high-flow coupler with the tool so you are not bottlenecked at the fitting. A filter-regulator-lubricator (FRL) keeps pressure stable and the air clean.
Need a spec?
If you tell us the tool list and how many run together, we will size the compressor, receiver and the coupler set to match — and we supply the air tools, fittings and air-preparation units to go with them. Send us your setup.
Frequently asked questions
Should I size by CFM or tank size?
Size by CFM (free-air delivery at 90 psi) first — that is what keeps tools powered. Tank size only smooths peaks between compressor cycles; a big tank on a weak pump still starves.
What is the difference between CFM and SCFM?
CFM is the raw volume; SCFM is that volume corrected to a standard pressure and temperature. Always use SCFM at your actual working pressure (usually 90 psi) when sizing.
How much margin should I add?
Add 25–30% on top of the summed average demand so the system is not running flat-out and tools keep full power under real-world peaks.
Why does my tool lose power with two running?
Because the compressor's delivery is below the combined SCFM demand, or the hose or coupler is too restrictive. Check pump delivery first, then hose ID and coupler flow rating.
Do I need a lubricator if my tools are oil-free?
Oil-free (vane) tools do not need a lubricator and should not be oiled. Standard vane air tools do need a mist lubricator; mixing the two up is a common cause of early wear.
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