What is CFM? CFM is the usual unit of measure for discharge air from a compressor.
CFM is the acronym for Cubic Feet per Minute. A compressor is said to have so many cubic feet of compressed air per minute (CFM) of flow from its discharge port.
When it comes to using compressed air in your plant or home workshop, you will want to know how many cubic feet per minute you can expect from the discharge port of your compressor. This will help determine if that air compressor has sufficient compressed air flow to power your air tools or other air-consuming applications.
To do that you need to know what CFM a particular device or tool will require to function within its design parameters. The device or tool will require a certain number of CFM at a specific air pressure, to work properly.
A rule of thumb is that each 1 HP motor size generates about 3-4 CFM of compressed air flow at about 90 PSI.
This air production by each HP of motor size is pretty much an industry standard, though it doesn’t apply as accurately to compressors under 10 HP. For compressors smaller than 10 HP, you will need to read the specifications for that particular unit to determine their exact flow and pressure rate capabilities, or use the “guestimate” of 2-3 CFM of discharge flow at 90 PSI, per HP of electric motor.
When you have sized all of your applications and totaled up all of the air you’re going to need now and for any prospective plant or air demand increases, and you are out searching for the right air compressor, you would divide the number of CFM you need by 4, and that will give you a rough idea of the horsepower rating of the compressor required.
Not all compressor manufacturer’s rate their compressor output the same way. You might see a compressor showing a discharge rate at what appears to be an acceptable CFM, but on closer inspection find that the figure is predicated on a much lower pressure than you might need.
Discharge rates in CFM at higher pressures are always quite a bit lower than discharge rates at lower pressures, for that same compressor.
Ensure that the unit you select will give you both the CFM you need, and the pressure your equipment demands to work properly for you.