SCFM versus ACFM versus ICFM

Actual air compressor capacity (ACFM) versus standard air capacity (SCFM) and inlet air capacity (ICFM)

SCFM - Standard Cubic Feet per Minute

It is common to rate the compressed air consumption in Standard Cubic Feet per Minute - SCFM.

The SCFM - Standard Cubic Feet per Minute - determines the weight of air to fixed or "Standard" conditions. There are several definitions of SCFM. The most common used in the United States is with "sea-level" properties:

• 14.696 Pounds per Square Inch (psia)
• 60 Degrees Fahrenheit (^oF) (520^oR)
• 0% Relative Humidity (RH).

Europeans normally use one ata and 0^oC as SCFM.

ACFM - Actual Cubic Feet per Minute

Unfortunately, real life "actual conditions" are seldom "standard conditions". When

• pressure is applied a volume of air - it gets smaller
• vacuum is applied to a volume of air - it expand

Actual air volume flow is often termed ACFM - Actual Cubic Feet per Minute.

Actual Cubic Feet per Minute - ACFM, depends on the

• pressure
• temperature
• humidity

of the actual air.

The conversion from SCFM to ACFM can be expressed as

ACFM = SCFM [P_std / (P_act - P_sat Φ)](T_act / T_std) (1)

where

ACFM = Actual Cubic Feet per Minute

SCFM = Standard Cubic Feet per Minute

P_std = Standard absolute air pressure (psia)

P_act = absolute pressure at the actual level (psia)

P_sat = Saturation pressure at the actual temperature (psi)

Φ = Actual relative humidity

T_act = Actual ambient air temperature (^oR)

T_std = Standard temperature (^oR)

Online SCFM - ACFM Calculator

The calculator below can used to calculate ACFM:

SCFM

Standard absolute air pressure (psia)

Actual absolute air pressure (psia)

Saturation pressure at the actual temperature (psia)

Actual relative humidity

Actual ambient air temperature (^oR)

Standard air temperature (^oR)

• temperature converter
• pressure converter

Example - SCFM to ACFM

The actual CFM of a compressor operating at "non-standard" conditions like

• elevation 5000 feet (1500 m) - atmospheric pressure P_act = 12.23 psia
• temperature 80^oF - absolute temperature T_act = 540^oR
• saturation pressure P_sat = 0.5069 psia
• relative humidity Φ = 80%
• demand 100 SCFM

can be calculated as

ACFM = 100 [14.7 (psia)/ (12.23 (psia) - 0.5069 (psia) 0.80)](540 (^oR⁾ / 520 (^oR))

    = 129.1  

ICFM - Inlet Cubic Feet per Minute

Inlet Cubic Feet per Minute - ICFM, is used by compressor vendors to establish conditions in front of additional equipment like inlet filter, blower or booster.

When air passes through the filter there will be a pressure drop. The conversion from ICFM to ACFM can be expressed as

ACFM = ICFM (P_act / P_f) (T_f / T_act) (1)

where

ICFM = Inlet Cubic Feet per Minute

P_f = Pressure after filter or inlet equipment (psia)

T_f = Temperature after filter or inlet equipment (^oR)

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