Understanding SCFM, ACFM, and ICFM: the difference flow rates?

What does CFM really mean?

When talking about air compressors, the term CFM (cubic feet per minute) is everywhere. It measures how much air a compressor can deliver at a given pressure or its flow rate. The higher the CFM, the more air is available for tools, processes, or equipment that need it.

But there’s a catch: not all CFM values are measured the same way. Because temperature, pressure, altitude, and humidity all affect airflow, different versions of CFM exist to describe performance more accurately. The three you’ll see most often are SCFM, ACFM, and ICFM.

Here’s what each one means and how they differ.

SCFM: Standard cubic feet per minute

SCFM measures a compressor’s airflow under standard conditions: a fixed temperature, pressure, and humidity. It’s the industry-standard reference point that allows an apples-to-apples comparison between compressors.

While those “standard” conditions rarely occur in real-world environments, SCFM is still the most practical figure for specification sheets because it keeps comparisons consistent and fair.

ACFM: Actual cubic feet per minute

ACFM reflects the real-world flow rate of a compressor under the actual operating conditions of your facility. This includes your site’s ambient temperature, elevation, and humidity.

Because these environmental factors vary so much, ACFM isn’t ideal for manufacturer specifications, but it’s extremely helpful when analyzing on-site performance or troubleshooting airflow issues.

To convert SCFM to ACFM, use this formula:

ACFM = SCFM [P_std / (P_act – Psat Φ)](T_act / T_std)

Where:

• Pstd = standard absolute pressure (psia)
• Pact = actual absolute pressure (psia)
• Psat = saturation pressure at actual temperature (psi)
• Φ = relative humidity
• Tact = actual ambient temperature (°R)
• Tstd = standard temperature (°R)

ICFM: Inlet cubic feet per minute

ICFM measures the air entering the compressor’s inlet, before it passes through any filters or intake equipment. Because pressure drops occur across those components, ICFM represents the air volume before any losses happen.

The conversion from ACFM to ICFM looks like this:

ICFM = ACFM (P_act / P_f) (T_f / T_act)

Where:

• Pf = pressure after filter or inlet equipment (psia)
• Tf = temperature after filter or inlet equipment (°R)

Why these airflow terms matter

When designing, purchasing, or maintaining a compressor system, everyone needs to speak the same language. Confusing SCFM, ACFM, and ICFM can lead to mis-sized systems, inefficient performance, or unexpected pressure drops.

Understanding these differences ensures you:

• Accurately compare compressor models
• Select the right system for your specific conditions
• Optimize performance and energy efficiency

Get help from a compressed air expert

Not sure which measurement applies to your setup? Our compressed air specialists can help you analyze your system and choose the right equipment for your conditions.

👉 Connect with an expert today to make sure your compressor delivers the performance you expect.