What CFM and PSI mean
Two numbers describe air tool needs:
- PSI (pounds per square inch) is pressure. It describes how hard the air is pushed.
- CFM (cubic feet per minute) is flow, the volume of air the tool uses in a minute. Compressors are rated for the CFM they deliver at a given pressure.
A compressor must supply at least the CFM the tool needs, at the pressure the tool needs. Tool makers usually publish a requirement such as “4 CFM at 90 PSI”. That means the tool uses about 4 cubic feet of air per minute when operated at 90 PSI. Compressor ratings are typically also stated at a pressure, most commonly 90 PSI, so the two can be compared directly.
Air tool consumption chart (typical ranges)
The figures below are approximate, typical ranges at about 90 PSI for common tools. Actual consumption varies by brand, model, size and how hard you use the tool, so always check the specifications printed on your tool or in its manual and treat this chart as a planning guide.
| Tool | Typical operating pressure | Approximate CFM | Use pattern |
|---|---|---|---|
| Brad nailer | 70-100 PSI | Under 1 | Intermittent |
| Finish nailer | 70-120 PSI | About 1-2 | Intermittent |
| Framing nailer | 70-120 PSI | About 2-4 | Intermittent |
| Stapler | 70-100 PSI | About 1-2 | Intermittent |
| 3/8 in. impact wrench | About 90 PSI | About 2-5 | Intermittent |
| 1/2 in. impact wrench | About 90 PSI | About 4-8 | Intermittent |
| Air ratchet | About 90 PSI | About 3-5 | Intermittent |
| Die grinder | About 90 PSI | About 4-8 | Continuous or long runs |
| Cut-off tool | About 90 PSI | About 4-10 | Intermittent to continuous |
| Dual-action (DA) sander | About 90 PSI | About 6-10 | Continuous |
| Orbital or palm sander | About 90 PSI | About 6-10 | Continuous |
| Paint spray gun | 20-90 PSI depending on type | About 4-15 | Continuous |
| Tire inflator or blow gun | About 90 PSI or less | About 1-5 | Short bursts |
Tools that run continuously, such as sanders, grinders and spray guns, are the ones that most often exceed what a small compressor can supply.
Intermittent vs continuous tools
Nailers, staplers and impact wrenches use air in short bursts, so the tank can recover between uses. A small compressor can often run them even if the tool’s peak consumption looks high. Sanders, die grinders, grinders and spray guns draw air all the time they are running, so the compressor’s delivered CFM has to keep up. This is the main reason shoppers find that a compressor that handles a nailer will fail at a sander.
How to calculate your air requirement
- List every tool you plan to use and note its CFM at its working pressure.
- If you will use more than one tool at the same time, add their CFM together. If you will only use one at a time, use the largest one.
- Add a safety margin. A common rule of thumb is about 25 to 50 percent extra, which allows for leaks, hose losses, wear and future tools.
- Compare the total with the compressor’s delivered CFM at the same pressure, not just its horsepower or its maximum PSI.
Example: a tool that needs 5 CFM at 90 PSI with a 30 percent margin works out to about 6.5 CFM, so look for a compressor rated at or above that figure at 90 PSI.
What does 7 CFM at 90 PSI mean?
It means the tool, or compressor, is rated for about 7 cubic feet of air per minute at a pressure of 90 PSI. For a tool, it is the air it uses. For a compressor, it is the air it can deliver at that pressure. Pressure and flow trade off, so a compressor’s CFM at 40 PSI is usually higher than at 90 PSI. Make sure you compare numbers at the same pressure.
How many PSI do air tools need?
Many air tools are designed for about 90 PSI at the tool, and some, such as nailers, work across a range. The manual gives the recommended and maximum pressures. Use a regulator to set the pressure and never exceed the tool’s maximum rating. For safety rules around pressurized tools, see our power tool injuries guide.
Tank size
The tank, or air receiver, stores air so the compressor does not need to run constantly. A larger tank helps with intermittent tools and reduces how often the motor cycles. It does not make up for a compressor that cannot deliver enough CFM for a continuous tool. Tank size is usually rated in gallons or liters. Buy for CFM first and then choose a tank size that suits how you work.
Tips for hoses and fittings
- Use hoses and couplers that are not undersized for the tool, because narrow hoses and restrictive fittings reduce the air reaching the tool.
- Keep hoses as short as practical, and check for leaks.
- Drain the tank regularly to remove moisture, following the manufacturer’s instructions.
- Wear eye and hearing protection, since air tools can be loud and can throw debris.
If you are choosing between power types for your shop, see corded vs cordless tools, and for a wider tool list see our beginner’s guide to power tools.