How to Size an Air Compressor for Your Workshop or Factory
Buying an industrial compressor based solely on horsepower is the most common—and most expensive—mistake business owners make. Here is how to correctly calculate your CFM and PSI requirements.
CFM vs. PSI: What's the Difference?
Before you can size a compressor, you must understand the two most important acronyms in the compressed air industry:
- PSI (Pounds per Square Inch) or Bar: This is the pressure. It determines how strong the air is. Think of this as the voltage in an electrical system. If a pneumatic tool requires 90 PSI to turn a bolt, feeding it 50 PSI means the tool simply will not work.
- CFM (Cubic Feet per Minute) or L/min: This is the flow. It determines how much volume of air is being delivered. Think of this as the amperage in an electrical system. If you run five tools simultaneously, you need a high CFM to keep them all spinning at once.
When sizing a compressor, you must meet the highest PSI requirement of your most demanding tool, and you must meet the total combined CFM requirement of all the tools that will be running at the exact same time.
Calculating Your Total Air Demand
Follow this simple formula to calculate your factory's required CFM:
- List all equipment: Write down every pneumatic tool, cylinder, and machine in your facility.
- Find the CFM rating: Look at the manufacturer's spec sheet for each tool to find its required CFM at a specific pressure (e.g., 10 CFM @ 90 PSI).
- Estimate the Usage Factor: Not every tool is used 100% of the time. If a spray gun is only triggered 40% of the hour, its usage factor is 0.4.
- Calculate total demand: Multiply each tool's CFM by its Usage Factor, and sum them all together.
- Add a buffer: Multiply your total by 1.25 (a 25% buffer) to account for system leaks and future factory expansion.
Use Our Free Calculator
Skip the manual math. Use our interactive online tool to select your equipment and instantly calculate your total facility CFM and recommended compressor size.
Oversizing: Why Bigger Isn't Always Better
A common trap is buying a massive industrial screw compressor "just to be safe." If you buy a 100 HP fixed-speed compressor for a factory that only needs 30 HP of air, the machine will constantly rapidly turn on and off (short-cycling).
Short-cycling destroys the electric motor, ruins the oil, and spikes your electricity bill because the motor draws massive inrush current every time it starts. If your demand fluctuates wildly, you should invest in a VSD (Variable Speed Drive) compressor, which can automatically slow its motor down to match lower demand without short-cycling.
Duty Cycle Considerations
The final factor in sizing is the duty cycle.
- If your workshop only uses air in short 15-minute bursts (like a small mechanic shop), a cheaper piston compressor with a 60% duty cycle is sufficient.
- If your factory runs continuous production lines 8 hours a day, a piston compressor will overheat and melt. You must select a rotary screw compressor, which has a 100% continuous duty cycle.
If you are unsure of your exact demand, the safest and most accurate method is to book a professional Compressed Air Data Logging Audit.