Start with the tool, not the compressor
List every pneumatic tool you intend to use and record its required airflow and pressure from the manufacturer. CFM figures are only meaningful when the pressure and measurement basis are clear.
Intermittent and continuous tools are different
An impact wrench used in short bursts can be supported by receiver storage and recovery between uses. A DA sander, grinder or spray gun may demand air for much longer periods, making sustained compressor output and duty cycle more important.
Allow sensible capacity above the calculation
Running permanently at the limit leaves little allowance for leaks, pressure loss, future tools or demand overlap. Headroom is useful, but buying an arbitrarily huge compressor can add cost, electrical requirements and noise without benefit.
Check the whole air path
Hose bore, fittings, regulators, filters, dryers and long pipe runs can restrict flow or create pressure drop. The compressor specification is only one part of the system.
Tool-demand figures and this guidance are planning aids. Confirm the actual airflow and pressure requirements of your tools and the compressor manufacturer’s delivered-air specification before buying or installing equipment.