ACFM

ACFM is actual cubic feet per minute, the literal volume of air moving through a compressor at the inlet under the real-world site conditions (pressure, temperature, humidity, altitude). Unlike SCFM, it is not normalized.

What it is

If you stood at the inlet of a compressor with a perfect flow meter, ACFM is what you would read. Because air density falls with altitude and rises with cold weather, the ACFM at a Colorado plant in summer is different from the ACFM at a Houston plant in winter, even on identical machines. The mass of air moved per minute is what physically performs work.

Why it matters

ACFM is the right number for sizing inlet ducting, filter housings, and intake silencers, because those components see real volumetric flow, not normalized flow. It is the wrong number for comparing two compressors against each other; that is what SCFM exists for. Manufacturers occasionally publish ACFM when the SCFM number is unflattering at altitude.

How it is used in our catalog

Catalog flow ratings are SCFM. ACFM enters the conversation when an installer is sizing inlet plumbing for an altitude install. Our installer directory filters by altitude experience for buyers above 3,500 ft.

Common questions

How do I convert ACFM to SCFM?

Apply the ratio of actual absolute pressure to standard absolute pressure, multiply by the ratio of standard absolute temperature to actual absolute temperature, and correct for inlet humidity. The result tells you how the same air would behave at the reference state.

Which number should appear on my purchase order?

SCFM at a stated discharge psig. Anything else is non-comparable.