CFM Calculator: How Much CFM Do I Need?
- Sullair dealer since 1984
- Serving industry since 1978
- No form fill, nothing gated
How do I size an air compressor?
To size an air compressor, add up the cfm ratings of the tools and processes that run at the same time, multiply by your average duty cycle, and add roughly 30 percent headroom for leaks and future growth. If you only know motor horsepower, figure roughly 4 to 5 cfm per HP at 100 psi for an industrial rotary screw unit. The calculator below does both, with every formula and assumption shown.
Calculate your required CFM
Enter how many of each tool run at the same time. The calculator sums their published ratings, applies your duty cycle, and adds 30 percent headroom.
| Tool or application | Typical cfm at 90 psi | Quantity in use |
|---|---|---|
| 5 cfm | ||
| 10 cfm | ||
| 4 cfm | ||
| 22 cfm | ||
| 10 cfm | ||
| 12 cfm | ||
| 35 cfm | ||
| 2 cfm | ||
| 3 cfm | ||
| 12 cfm |
Know the motor size but not the tool demand? Estimate delivered cfm from horsepower using the published rules of thumb below.
The formulas and every assumption, in the open
These are the only formulas the calculator uses. Nothing is hidden or weighted.
| Step | Formula | Basis |
|---|---|---|
| Tool demand | Required cfm = (sum of simultaneous tool cfm) x duty cycle x 1.3 | Tool ratings are typical published manufacturer figures at 90 psi, listed in the table above. The 1.3 factor is 30 percent headroom for leaks and growth, the allowance we use in every sizing review. |
| CFM from HP, rotary screw | Delivered cfm = HP x 4 to 5 | Widely published industry rule of thumb for industrial rotary screw compressors at 100 psi. Verify against the model datasheet. |
| CFM from HP, piston | Delivered cfm = HP x 3 to 4 | Widely published rule of thumb for reciprocating compressors, which deliver less air per HP than screws at the same pressure. |
Limits of the estimate: tool ratings vary by brand, duty cycles vary by shift, and cfm falls as pressure rises. Treat the output as a starting range, not a purchase spec.
Match your CFM to a compressor size
| Required cfm (with headroom) | HP class | Typical machine |
|---|---|---|
| Up to 40 cfm | 5 to 10 HP | Sullair ES-6 S-energy or ShopTek |
| 40 to 110 cfm | 15 to 25 HP | Sullair S-energy 15-25 |
| 110 to 270 cfm | 30 to 60 HP | Sullair S-energy 3000PB-4500VB |
| 270 to 470 cfm | 75 to 100 HP | Sullair SN Series |
| 470 to 1,000 cfm | 125 to 200 HP | Sullair LS Series |
| 1,000 cfm and up | 250 to 350 HP | Sullair TS Series |
Browse the full rotary screw compressor lineup or the complete product catalog by model. Sizing a portable job site unit instead? Start with the portable diesel compressor page.
CFM sizing questions, answered first
How much CFM does an air compressor make per HP?
Plan on roughly 4 to 5 cfm per HP at 100 psi for an industrial rotary screw compressor, and roughly 3 to 4 cfm per HP for a reciprocating piston unit. So a 25 HP rotary screw delivers about 100 to 125 cfm, while a 25 HP piston machine delivers about 75 to 100 cfm. Actual output varies by model, so confirm the datasheet cfm at your working pressure before buying.
How do I calculate the CFM I need for my shop or plant?
Add up the rated cfm of the tools and processes that run at the same time, multiply by your average duty cycle, then add about 30 percent headroom for leaks and growth. For example, three stations at 12 cfm each running at 75 percent duty is 27 cfm, and 27 times 1.3 is about 35 cfm. That is the number to match against compressor datasheets, and an air audit confirms it with measurements.
Does PSI affect how much CFM I get?
Yes. A compressor delivers less cfm as discharge pressure rises, and every 2 psi of extra pressure costs about 1 percent more energy. Size the system at the pressure your most demanding tool actually needs, usually 90 to 125 psi, and compare compressor ratings at that same pressure. Raising the whole plant header to satisfy one high pressure process is usually the expensive way to solve it.
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These are estimates. An air audit gives you measurements.
A week of logged data on your actual system beats any rule of thumb. Our engineers run no-obligation compressed air audits across 14 Midwest locations.