Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

• the most efficient way to navigate the Engineering ToolBox!

# Air - SCFM versus ACFM and ICFM

### SCFM - Standard Cubic Feet per Minute

It is common to rate 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 the "sea-level" properties:

• 14.696 Pounds per Square Inch (psia)
• 60 Degrees Fahrenheit ( oF) (520 o R)
• 0% Relative Humidity (RH)

Europeans normally use one ata and 0 oC as SCFM.

Note that the The Compressed Air & Gas Institute and PNEUROP have adopted the definition used in ISO standards with dry (0% relative humidity) air at 14.5 psia (1 bar) and 68 oF (20 oC).

### ACFM - Actual Cubic Feet per Minute

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 expands

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

The 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

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 ( o R)

T std = Standard temperature ( o R)

Note!

P sat Φ ƒ < P act

.

### Related Mobile Apps from The Engineering ToolBox

- free apps for offline use on mobile devices.

### Online SCFM - ACFM Calculator

The calculator below can used to calculate ACFM:

#### 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 o R
• saturation pressure P sat = 0.5069 psia
• relative humidity Φ = 80%
• demand: 100 SCFM

can be calculated as

ACFM = (100 SCFM) [(14.7 psia) / ((12.23 psia) - (0.5069 psia) (80 / 100))]((540 o R ) / (520 o R))

= 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 ACFM to ICFM can be expressed as

ICFM = ACFM (P act / Pf ) (Tf / T act )                                               (2)

where

ICFM = Inlet Cubic Feet per Minute

Pf = Pressure after filter or inlet equipment (psia)

Tf = Temperature after filter or inlet equipment ( o R)

### Note!

The Ideal Gas Law is accurate only at relatively low pressures and high temperatures. To account for the deviation from the ideal situation, another factor is included. It is called the Gas Compressibility Factor, or Z-factor . This correction factor depends on the pressure and temperature for each gas considered.

The True Gas Law, or the Non-Ideal Gas Law, becomes:

P V = Z n R T  (3)

where

Z = Gas Compressibility Factor

n = number of moles of gas present

.

### Air Volume Conversion Factors

Air volume conversion factors related to air with temperature 70°F (21.1°C) :

Air volume conversion factors related to air with temperature 70°F (21.1°C)
Air TemperatureFactor
°F°C
0 -17.2 1.152
10 -12.2 1.128
20 -6.7 1.104
30 -1.1 1.082
40 4.4 1.060
50 10.0 1.039
60 15.6 1.019
70 21.1 1.000
80 26.7 0.981
90 32.2 0.964
100 37.8 0.946
110 43.3 0.930
120 48.9 0.914
130 54.4 0.898
140 60.0 0.883
150 65.6 0.869
160 71.1 0.855
170 76.7 0.841

## Related Topics

### • Gases and Compressed Air

Properties of air, LNG, LPG and other common gases. Pipeline capacities and sizing of relief valves.

## Related Documents

### Air Compressor - Power Cost per Year

Yearly power cost for operating an air compressor.

### Air Compressors - Maximum Air Flow vs. Inlet Pipe Size

Inlet pipe size and maximum air flow.

### Air Temperature, Pressure and Density vs. Altitude

Elevation above sea level and air temperature, pressure and density.

### Air Tools - Air Consumption

Air consumption of air tools.

### Atmospheric Pressure vs. Elevation above Sea Level

Elevation above sea level - in feet and meter - with barometric and atmospheric pressure - inches mercury, psia, kg/cm2 and kPa.

### Moist Air - Relative Humidity

Relative humidity in moist air is the ratio of partial vapor pressure to air pressure.

### Non-ideal gas - Van der Waal's Equation and Constants

The van der Waals constants for more than 200 gases used to correct for non-ideal behavior of gases caused by intermolecular forces and the volume occupied by the gas particles.

### Rating of Air Compressors and Air Equipment

Common rating terms for air flow capacity are ICFM, FAD, ANR, SCFM or nl/min.

### The Ideal Gas Law

The relationship between volume, pressure, temperature and quantity of a gas, including definition of gas density.

### Turbo Machines - Specific Work done by Pumps, Compressors or Fans

Calculate specific work done by pumps, fans, compressors or turbines.

### Types of Air Compressors

Reciprocating, rotary screw and rotary centrifugal air compressors.

### Vacuum Pipes - Pressure Loss vs. Air Flow

Calculate pressure drops in vacuum pipe lines.

### Water - Boiling Points at Vacuum Pressure

Online calculator, figures and tables giving the boiling temperatures of water in varying vacuum, SI and Imperial units.

### Water - Saturation Pressure vs. Temperature

Online calculator, figures and tables with water saturation (vapor) pressure at temperatures ranging 0 to 370 °C (32 to 700°F) - in Imperial and SI Units.

## Search Engineering ToolBox

• the most efficient way to navigate the Engineering ToolBox!

## SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!