Most compressors are oversized. The result: short cycling, premature wear, and operating costs higher than they need to be. Here's the field-tested method we use to size systems correctly.
Sizing a compressed air system isn't complicated, but it requires being honest about your actual demand — not the worst-case demand the salesperson at the manufacturer's showroom would like you to imagine. Oversized systems short-cycle, run inefficiently, and waste money for the life of the equipment.
List every air-consuming device in the shop: impact wrenches, paint guns, sanders, blow guns, pneumatic chucks, plasma cutters, tire machines, anything that breathes. For each one, find the manufacturer's CFM-at-PSI rating. (CFM = cubic feet per minute. PSI = pounds per square inch. Most pneumatic tools spec at 90 PSI.)
| Tool | Typical CFM @ 90 PSI |
|---|---|
| 1/2" impact wrench | 4–5 |
| 3/8" impact wrench | 3–4 |
| Air ratchet | 4 |
| Random orbital sander | 8–10 |
| DA sander (heavy) | 12–15 |
| HVLP paint gun | 10–14 |
| Plasma cutter (40A) | 5–7 |
| Pneumatic chuck | 3 |
| Air drill | 4 |
| Cut-off tool | 5–7 |
Not every tool runs continuously. An impact wrench might run 30 seconds out of every 5 minutes — a 10% duty cycle. A sander on a paint prep job might run 70% of the time it's in someone's hand. A paint gun running constantly during a spray job is at 100%.
Multiply each tool's CFM by its realistic duty cycle, then sum the results. That's your average demand. Now multiply that average by 1.25 to give yourself headroom for simultaneous tool use and air leaks (more on leaks below).
Every compressed air system has leaks. The industry rule of thumb is that a system without active leak management runs 20–30% wasted air. Our leak surveys typically find 25%. If you've never had a leak audit done, add another 25% to your demand calculation — or better, factor leak management into the system from day one.
Tank size matters most for piston compressors and intermittent-demand systems. The tank stores air so the compressor doesn't have to run continuously. Larger tank = fewer starts/stops = longer compressor life.
We see this constantly. Someone buys a 25 HP rotary screw because they 'want headroom for future expansion.' The compressor short-cycles for the next eight years, builds heat unevenly, and the air-end wears prematurely. Buy what you actually need with 25% headroom — not a unit twice your demand.
If you genuinely expect to expand later, the right answer is a properly sized current unit plus a second compressor when the time comes — staged in parallel with sequencing controls. Two 15 HP units running 50% each is more efficient and more redundant than one 30 HP unit cycling on and off.
| HP | Approx CFM @ 90 PSI | Typical fit |
|---|---|---|
| 5 HP | 15–20 | Single-bay shop, 1–2 simultaneous tools |
| 7.5 HP | 23–28 | 2–3 bays, light continuous use |
| 10 HP | 33–40 | 3–4 bays or one paint booth |
| 15 HP | 50–58 | Auto body shop, mid-size manufacturing |
| 25 HP | 85–100 | Production manufacturing, multiple booths |
| 50 HP | 180–220 | Industrial production |
| 100 HP | 380–460 | Heavy industrial / large facility |
Tell us what you're running and we'll spec the right equipment, install it, and keep it running.
Rotary screw compressors run continuously, piston compressors don't. That's the simple answer. The longer answer involves duty cycle, noise, maintenance burden, and what happens to your tools when air quality degrades.
Most shops need a refrigerated dryer. A small minority need desiccant. The wrong choice either wastes money on capability you don't use or leaves moisture in lines that ruins downstream equipment.