Why CFM is the useful starting point
Pneumatic tools consume air. Adding realistic tool demand gives you a more useful compressor requirement than choosing from tank litres or motor power alone.
Do not mix unlike figures
A tool requirement and compressor output need to be comparable. Check whether figures are stated in CFM or litres per minute, the operating pressure, and whether the compressor number is displacement or delivered air.
Add demand carefully
If two tools genuinely operate together, their airflow requirements may need to be combined. If one operator uses them sequentially, simply adding every tool in the garage can grossly oversize the system.
Use the result as a specification, not a guarantee
Actual performance also depends on duty cycle, pressure control, receiver, pipework, fittings, leaks and maintenance. Verify the final design with the compressor and tool manufacturers or a competent compressed-air supplier.
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.