Friday, October 7

The CFM vs. SCFM vs. ACFM vs. ICFM Monster

We frequently get asked questions about the difference between CFM, SCFM, ACFM, and ICFM and notice it
has been populating our search queries too! We’re here to talk about these acronym monsters and
simplify them for you so they are less scary and confusing.


CFM is quite simple. It stands for cubic feet per minute and is used in reference to your air compressor’s flow rate. The higher the CFM number is, the more air your compressor can supply. This number is used as a baseline, assuming all environmental factors are all constant including temperature, density, climate, humidity, and all other factors that can impact an environment. Location, altitude, and seasons are all large factors that can severely impact the compressor’s environment. Because of the lack of specifics that go into this measurement, it is rarely used in compressed air analytics.


We know that all environments are not the same and compressors located in different areas will not experience the same environmental factors. Because of this, we use SCFM for a more accurate indicator of a compressors air capacity. SCFM stands for standard cubic feet per minute and refers to the flow rate at standard conditions. Basically, SCFM adjusts for a standard cubic foot of air to fill one cubic foot of volume to give an easy to follow 1:1 ratio. While “standard” conditions will not always be met, this metric allows us to produce a more practical measurement for comparison between compressor choices. However, SCFM measures weight not volume. It does adjust for psia, temperature, and relative humidity- unlike CFM.


Another term frequently used in the compressed air industry is ACFM. ACFM stands for actual cubic feet per minute, and it is the most precise measurement of your compressor’s flow rate out of CFM, SCFM, and ACFM because it takes into consideration the varying environmental conditions your compressor may endure. However, while this is a more precise description, it is also impossible to directly state ACFM capacity on a label on each compressor as all environments are extremely different whether it be the room next door or a completely different continent. Therefore, we, the compressed air experts, utilize a formula to convert SCFM to ACFM. The formula is as followed:

ACFM = SCFM [Pstd / (Pact – Psat Φ)](Tact / Tstd)
ACFM = Actual Cubic Feet per Minute
SCFM = Standard Cubic Feet per Minute
Pstd = standard absolute air pressure (psia)
Pact = absolute pressure at the actual level (psia)
Psat = saturation pressure at the actual temperature (psi)
Φ = Actual relative humidity
Tact = Actual ambient air temperature (oR)
Tstd = Standard temperature (oR)

This is an entirely different monster that looks confusing at first, but our compressed air exerts are here to help!


Finally, ICFM refers to the conditions of the flow that are met at the inlet valve of your compressor. In general, the filters within your compressed air system and the inlet will cause the pressure to drop as air gets pulled through. This drop in pressure is what ICFM accounts for at the inlet as air begins to be pulled through the system. To find ICFM, you need to convert ACFM to ICFM by using another compressed air expert formula:

ICFM = ACFM (Pact / Pf) (Tf / Tact)
ICFM = Inlet Cubic Feet Per Minute
Pf = Pressure after filter or inlet equipment (psia)
Tf = Temperature after filter or inlet equipment (°R)

Now that you know the difference between all four acronyms, you can better understand how we figure out your compressor’s flow rate- a crucial step in understanding your facilities air demand. CFM, SCFM, ACFM, and ICFM aren’t scary monsters once you get to know them, but if you still have hesitations or need help with other compressed air “monsters.” Reach out to Zorn Compressor today and we will have a local representative sent out to your facility to help.



Zorn is the Midwest leader of custom, engineered compressed air and vacuum solutions. We provide the best customer experience by understanding your applications and needs and offering an unparalleled commitment to customer satisfaction. 

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Our compressed air experts look forward to meeting you to discuss your equipment and support needs. Please contact us directly at (262) 695-7000 with any questions or to schedule service for your system moving forward.

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