SCFM stands for standard cubic feet of air per minute. This term is used to measure air flow rate. SCFM is the air flow rate when corrected for current temperature and pressure. You can calculate SCFM from actual cubic feet per minute (ACFM) if the air pressure, temperature and altitude are known. Heating, vacuum and air conditioning equipment sizing require SCFM calculations. For example, calculating SCFM helps determine how big the AC needs to be to keep a building cool.

## If ACFM in English Units Is Known

Divide the actual pressure by the standard pressure.

Divide the standard temperature by the actual temperature.

Multiply these two results by ACFM to get the SCFM.

## If ACFM in Metric Units Is Known

If you have the ACFM in metric units, such as absolute pressure units and temperature in Kelvin, the SCFM equation becomes the SCF. The ACFM becomes the ACF. The SCF is calculated using the following method. First, divide the actual pressure by the standard pressure.

Divide the standard temperature by the actual temperature.

Multiply these two results by ACF.

The result is called the SCF. This is the metric equivalent to the SCFM

## To Calculate SCFM from the Inlet Cubic Feet Per Minute Value

To calculate the SCFM produced by a motor and drive pump with a 1-1 ratio, multiply the RPM by the CFD (cubic foot displacement).

When using air blowers, 1 horsepower of power is needed to compress 4 standard cubic feet of atmosphere per minute in 1 cubic foot of space. In standard atmospheric conditions, each horsepower the blower is using to blow the air is roughly equal to 4 SCFM. For a 100 horsepower blower, approximately 400 SCFM are passing through the vent per minute.

The standard temperature used in the English and United States SCFM calculation is room temperature, 60 to 70 degrees Fahrenheit. In SI calculations, the SCF is usually calculated at 0 degrees Celsius, the freezing point of water. This means that given the same set of real-life conditions but differing standards of temperature can result in slightly different SCF and SCFM values.

To take humidity into account with the SCFM calculation, more complex calculations that involve water saturation factors are required.

Divide the actual air pressure by the air pressure recorded in the air flow after inlet or filter.

Divide the temperature at the inlet by the actual environmental temperature.

Multiple these two results with the ICFM value. The result of this is the SCFM.

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#### Photo Credits

- in the air image by katja kodba from Fotolia.com