ACFM to ICFM Converter
ACFM (Actual Cubic Feet per Minute) and ICFM (Inlet Cubic Feet per Minute) are both volumetric flow rates measured at the actual temperature and pressure of the measurement point —...
Formula
Source: Engineering Toolbox, CAGI standards | Last reviewed: June 8, 2026
Examples
1 ACFM
= 1 ICFM
1 ACFM = 1 ICFM at same conditions
100 ACFM
= 100 ICFM
500 ACFM
= 500 ICFM
Quick Reference Table
| ACFM | ICFM |
|---|---|
| 1 | 1 |
| 10 | 10 |
| 50 | 50 |
| 100 | 100 |
| 500 | 500 |
| 1000 | 1000 |
Where is this used?
When flow is measured at the compressor inlet, ICFM and ACFM are equivalent.
For flows measured elsewhere in the system (discharge, aftercooler), use the SCFM/ACFM converters with appropriate temperature and pressure corrections.
In the design of compressed air distribution systems per CAGI B186.1 and the DOE Compressed Air Challenge, the ICFM at the compressor inlet is the most useful measurement for tracking the plant's actual demand and for capacity planning, because it represents the mass of air the compressor is delivering regardless of the discharge pressure.
A 100 hp compressor with a nameplate of 400 SCFM at 100 psig has an ICFM of about 400 × (P_std / P_inlet) = 400 × 1 = 400 ICFM at sea-level standard inlet conditions, but the same compressor at 5,000 ft elevation and 90°F inlet temperature has an ICFM of 400 × (14.696/12.23) × (528/550) = 462 ICFM — the compressor is moving 15% more actual cubic feet of air at altitude to maintain the same mass flow.
The CAGI Compressed Air Audit program and the US DOE Compressed Air Challenge use ICFM measurements at the compressor inlet (typically with a pitot tube traverse or insertion thermal mass flow meter) as the primary audit metric, with the ICFM compared to the SCFM nameplate to assess the compressor's current health and efficiency.
In HVAC and process air handler applications, the ICFM at the fan inlet (with the inlet bellmouth, screen, and ductwork losses accounted for) is the standard fan performance measurement, and the SCFM equivalent is used for comparing to the fan's published performance curves (which are in SCFM at standard air density).
A 30,000 CFM air handler with an inlet temperature of 100°F (summer conditions, no evaporative cooling) has an ICFM of 30,000 but a SCFM of about 28,500 — the conversion is required for fan performance verification per AMCA Standard 210 and ASHRAE Standard 111.
Engine and turbine inlet airflow measurement per ASME PTC 22 (gas turbines) and the ICFM at the engine inlet is the primary test measurement, with the conversion to mass flow (kg/s) for the engine performance map and to SCFM for the engine's published specifications (which are typically in SCFM at standard day conditions of 59°F, 14.696 psia, and 60% RH per ISO 3977).
Frequently Asked Questions
What is the difference between ACFM and ICFM?
ACFM is a general term for actual cubic feet per minute at any measurement point. ICFM specifically refers to the flow measured at the compressor inlet flange. At the same conditions, the numeric value is identical.
When should I use ICFM vs ACFM?
Use ICFM when referring to compressor inlet conditions for performance testing and specification. Use ACFM as a general term for any flow measurement point in the system.
How does ICFM relate to SCFM?
ICFM is an actual flow at inlet conditions; SCFM is the same mass flow normalized to standard conditions. Convert ICFM to SCFM using temperature and pressure correction: SCFM = ICFM × (T_std/T_actual) × (P_actual/P_std).
Reviewed for accuracy
· Last reviewed: June 8, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.