Air Compressor Size Calculator
This air compressor size calculator works out the CFM your compressor must deliver for the air tools you run. Enter the CFM and number of up to three tool types, how many run at once, and allowances for leaks and growth, and the air compressor size calculator returns the CFM needed at 90 psi and an approximate motor size.
Results
The Air Compressor Size Calculator is part of our Fluids collection. Browse more fluids to size, convert, and check your work alongside this tool.
What the air compressor size calculator does
A compressor is sized by the airflow it delivers at working pressure, not by its tank or horsepower alone. The air compressor size calculator adds the CFM of every tool, scales it by how many run at the same time, adds air lost to leaks, then adds a margin for growth. The result is the CFM at 90 psi to look for on the compressor spec plate.
Compressor CFM requirements
The calculator follows the usual sizing method:
The horsepower estimate uses a common rule of about 4 CFM per horsepower at 90 to 100 psi for small piston and rotary screw units; check the maker data for the model you buy.
Air compressor size calculator example
A shop with a 5 CFM impact wrench, an 11 CFM orbital sander, and two 2.5 CFM nailers, 60% in use at once:
That is about 510 L/min, or a compressor of roughly 4.5 hp. A single sander running nonstop sets a floor of 11 CFM on its own.
How to use the air compressor size calculator
Look up the air use of each tool at 90 psi on its label or manual. Enter up to three tool types with their CFM and quantity. Set the use factor to the share of tools running at the same moment, from 100% for one continuous tool such as a sander to 30 to 60% for a busy shop. Keep about 10% for leaks and 25 to 30% margin, then press Calculate.
Reading the compressor size calculator result
Choose a compressor rated at or above the CFM shown, measured at 90 psi, since ratings at 40 psi look higher but do not drive tools. Continuous tools such as sanders, grinders, and spray guns need the compressor to keep up without a break, so their full CFM counts. Tools that fire briefly, such as nailers and impact wrenches, draw from the tank, which is why a larger tank helps with short bursts but cannot fix an undersized pump.
When to use an air compressor CFM calculator
- Buying a compressor for a home garage or shop
- Checking whether a compressor can run a sander or spray gun
- Planning compressed air for a small factory line
- Comparing piston and rotary screw options
- Adding new tools to an existing system
Common air compressor size calculator mistakes
- Comparing CFM at 40 psi. Use the 90 psi rating.
- Sizing by tank size. Tanks do not add CFM.
- Using 100% use factor for bursts. Nailers rarely run together.
- Ignoring leaks. Leaks waste air all day.
Tips for compressor CFM requirements
- Size around the largest continuous tool.
- Use short, large diameter hoses to keep pressure up.
- Drain tanks daily and fix leaks with soapy water checks.
How to size an air compressor for a shop
The hardest number is the use factor. One person in a home garage rarely runs two tools at once, so the largest single tool usually decides the size, with a margin. A body shop with several bays may have half its tools running at any moment, and a production line with cylinders cycling constantly runs close to 100%. Logging the compressor run time for a week is the best way to find the real demand on an existing system. Machines with cylinders add steady demand, which the pneumatic cylinder calculator works out per minute.
Air compressor sizing: piston versus rotary screw
Piston compressors suit intermittent use and small shops; they should not run continuously at full load, so many makers suggest a duty cycle limit. Rotary screw compressors are built to run all day and deliver more CFM per horsepower at steady load. Above about 10 hp, many shops switch to rotary screw units on three phase power. Size the motor circuit for the compressor with the motor FLA calculator, and fix leaks before buying bigger: a leaky shop can lose a fifth or more of its air.
Air tool CFM chart
Typical air use at 90 psi. Values vary by brand, so use the tool label when you have it:
| Tool | Typical CFM at 90 psi | Duty |
|---|---|---|
| Brad or finish nailer | 0.3 to 1 | Short bursts |
| Framing nailer | 2 to 3 | Short bursts |
| 3/8 in ratchet | 3 to 5 | Short bursts |
| 1/2 in impact wrench | 4 to 6 | Short bursts |
| Die grinder | 4 to 6 | Continuous |
| Air hammer | 3 to 5 | Intermittent |
| Dual action sander | 8 to 13 | Continuous |
| HVLP spray gun | 6 to 15 | Continuous |
Air Compressor Size Calculator FAQ
What size air compressor do I need?
Add the CFM of the tools you use at the same time, add about 10% for leaks and 25 to 30% margin, and buy a compressor rated for that CFM at 90 psi.
How do I convert compressor hp to CFM?
A rough rule is about 4 CFM per horsepower at 90 psi. Spec plates vary, so compare rated CFM at 90 psi rather than horsepower.
Does a bigger tank give more CFM?
No. A tank stores air for short bursts but does not raise the pump output. Continuous tools need enough CFM from the pump.
Why rate at 90 psi?
Most air tools are rated at 90 psi. A compressor CFM rating at a lower pressure looks higher but will not run the tools.