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Buying an air compressor starts with one number: how much air do your tools actually need? Guess too small and the tank drains faster than the pump refills it, pressure sags, and tools go soft mid-job. Guess too big and you overspend on a pump you never stretch. This calculator totals the CFM of the tools you run at the same time, adds the headroom margin, and converts for duty cycle so you can size the unit correctly the first time.
The CFM figures below are typical values from manufacturer sizing charts. Your tool’s data plate always wins — edit any number to match your gear.
| Air tool | CFM @ 90 PSI | Qty | Use it? |
|---|
How to read your result
Total tool CFM is the air your checked tools draw at the same time. Required CFM at 90 PSI adds your headroom margin for leaks, hose loss and hot weather. Rated CFM to look for divides by duty cycle — a 50% duty-cycle pump must be rated roughly twice your continuous draw, because it rests half the time.
Typical air-tool CFM requirements
| Tool | Typical CFM | Typical working PSI |
|---|---|---|
| Brad nailer | 1–2 | 70–90 |
| Framing nailer | 1–2 | 70–90 |
| Blow gun | ~3 | 70–90 |
| Tyre inflator | 2–3 | 100–150 |
| Air ratchet | 3–5 | 90–100 |
| ½″ impact wrench | 4–5 | 90 |
| Conventional spray gun | 4–8 | 30–50 |
| HVLP spray gun | ~15 | 40–60 |
| Die grinder | 4–7 | 70–90 |
| Pneumatic angle grinder | 5–8 | 90 |
| Pneumatic random-orbit sander | 8–12 | 90 |
These are starting points only — always check your own tool’s data plate, because models vary. Full method: our air compressor CFM guide works the same maths by hand with a framing nailer + blow gun example.
Frequently Asked Questions
Does a bigger tank give me more CFM?
No. The tank stores air; the pump makes it. A bigger tank stretches bursts and rests the pump, but once the stored air is gone, output equals pump CFM. Tools going soft after a minute mean you need CFM, not litres.
Can I run two air tools at the same time?
Yes, if the maths works: add both CFMs, apply the 1.3–1.5 headroom margin, and check the result against the compressor’s rated CFM at 90 PSI after duty-cycle conversion. A nailer plus a blow gun suits a mid-size unit; a sander plus a grinder needs serious CFM.
Why does my impact wrench feel weak when the gauge still reads 90 PSI?
That is CFM starvation: the gauge shows static tank pressure, but under load a small pump cannot sustain the flow, so pressure at the tool collapses on the trigger. Fix it with more delivered CFM — or a shorter, wider hose — not more tank pressure.
Keep going: compressor guides
Once the calculator has your number, our 2026 air compressor buying guide picks through the options, and our generator sizing calculator runs the same add-it-all-up maths for watts if your compressor will run off a generator.