Air Compressor Basics – CFM Ratings Explained

One of three major determinants of air compressor, either portable type or standing type for industrial use, is the CFM rating, which stands for cubic feet per minute. CFM indicates the flow rate at a specified pressure level. In other words, CFM is always given with a pressure level.

A higher CFM is better than a lower CFM as it indicates that it can provide more flow at a given pressure level. And, in some cases, a higher CFM is necessary given the components (e.g. actuators, drills, etc.) in the pneumatic system.

2. ‘Inlet’ vs. ‘Outlet’ Air Compressor CFM Ratings (and marketing Mumbo-Jumbo)

Please be aware that there is industry-discrepancy over how CFM ratings are measured and marketed, leading to consumer dissatisfaction over a compressors flow performance. This is due to some manufacturers measuring CFM at the compressor inlet whereas others measure at outlet. As a matter of mechanics, ‘inlet’ CFM ratings will always be higher than the ‘outlet’ rating for the same compressor.

Whilst a manufacturer may advertise 4.0 CFM @ 90 PSI, if a tool operates at 90 PSI, then (given Boyle’s law), the flow at the tool will be only 0.8 CFM. There is a large discrepancy between the advertised 4.0 cfm and the 0.8 cfm at the tool. It is important to understand that CFM ratings are at the compressor inlet and not outlet. Accordingly, if your component or tools requires a higher than CFM, then make sure that your compressor CFM is appropriate. If the CFM rating is at the inlet pressure, then Boyle’s law must be used.

As a consumer, please be aware which type of CFM rating the manufacturer is advertising.