Sizing a compressor is mainly about two numbers: airflow and pressure. Airflow is commonly quoted in CFM, while pressure is quoted in PSI, bar or kPa. A compressor must supply enough of both at the point of use, not just at the machine outlet.
Key points
- Start with the tools, not the compressor
- Add the airflow of tools that will run at the same time
- Use the highest required operating pressure
- Add practical headroom for hose losses and changing demand
A practical sizing sequence
Write down every air consumer that may operate simultaneously. Add their stated free-air requirements, then identify the highest pressure any one tool needs. A compressor rated for enough CFM but too little pressure is not suitable, and neither is a high-pressure machine with inadequate free-air delivery.
For intermittent tools, a supplier may consider diversity of use rather than assuming every tool draws maximum air continuously. For critical continuous processes, size more conservatively and discuss backup capacity.
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