Standard Cubic Feet per Minute or scfm is the measure of airflow or air volume within a system (in this case, from an air compressor) of a column of air at a pressure of 14.7 psi (i.e. atmospheric pressure) at 68oF (i.e. room temperature). This unit of measurement is rarely used with air compressors since practically speaking, air compressors are rarely used to produce uncompressed (atmospheric / 14.7 psi) airflow. Often it is used in error to represent cubic feet per minute (cfm).
Cubic Feet per Minute (cfm) is the measure of airflow or air volume within a system in which the air pressure and temperature of the air column have not been specified. In the case of air compressors and air tool ratings, the pressure is usually specified together with the air volume measurement (eg. “4 cfm @ 90 psi”), and the temperature is usually assumed to be room temperature.