CFM and PSI solve different parts of the sizing problem. CFM tells you how much air the compressor can deliver; PSI tells you the pressure at which it can deliver it. A tool can perform poorly when either figure is inadequate.
Key points
- CFM describes volume of air
- PSI describes pressure
- A high-PSI machine can still be short of airflow
- Tool manufacturer data should take priority
Why both numbers matter
Think of pressure as the force available to the tool and CFM as the volume of air available to keep it working. A large air-hungry nozzle can overwhelm a compressor even when the pressure gauge initially looks acceptable. Conversely, a high-flow low-pressure machine may not suit a process that needs substantially higher pressure.
Compare specifications at the same stated pressure. Compressor output can change with operating pressure, so a headline CFM figure should not be separated from the pressure at which it is rated.
How to specify the job
Start with the equipment or process that will consume the air. Record the number of tools that may run at the same time, each tool's required airflow, and the highest operating pressure. For industrial temporary-air jobs, also note required air quality, duty cycle, connection size and whether the process can tolerate interruption.
Airflow, pressure and operating margin
Compressor capacity is usually described by airflow and pressure. In Australia you will commonly see airflow in CFM or m³/min and pressure in PSI or bar. The compressor must meet both requirements at the point of use. Long hose runs, fittings, filters and simultaneous demand can reduce effective performance, so a practical sizing margin is useful.
What to ask the hire supplier
Machine
Confirm rated free-air delivery, working pressure, fuel or electrical requirements and whether the exact model may vary.
Accessories
Ask about hoses, manifolds, aftercoolers, dryers, filtration, receivers, fittings and any tool-specific accessories.
Logistics
Confirm towing or delivery, access, placement, refuelling, collection, operating hours and any site induction requirements.
Safety
Follow the supplier's risk assessment and operating manual. Verify hose, coupling and accessory pressure ratings.
Use the sizing calculator
If your application is based on pneumatic tools, our calculator can total approximate airflow and suggest a compressor class. It is a planning tool only; final selection should be confirmed against the actual equipment specifications.
Open compressor calculator