When rating the gas flow capacity of pressurized equipment such as air compressors, you should use the standard cubic foot per minute (SCFM). SCFM is a commonly-accepted national standard based on the amount of air that would flow through the equipment if it were at sea level and the gas was at a standard temperature and had 0 percent relative humidity. But these conditions rarely exist when you take your measurements. When you measure gas flow under actual conditions, you get the actual cubic feet per minute (ACFM). To standardize your measurements, you must convert ACFM to SCFM.

Enter the ACFM into your calculator.

Press the "x" key.

Enter "((psig + 14.7)/14.7)." Replace "psig" with your equipment's gauge pressure. The number 14.7 is the standard atmospheric pressure at sea level. Include all the parentheses in the correct order.

Press the "x" key.

Enter "((68 +460)/(T + 460))." Replace "T" with the actual temperature at the time of testing. This formula uses 68 as the standard temperature in Fahrenheit, but some people use other temperatures when calculating SCFM.

Press "=" to get the SCFM.

Double check your calculation with the complete formula: "SCFM = ACFM x ((psig + 14.7) / 14.7) x ((68 +460) / (T + 460))."