What is SCFM vs. CFM?
The term CFM is often confusing and difficult to define. One definition does not satisfy all conditions we encounter when dealing with applications throughout the world.
Some air tool manufacturers use CFM to rate their tools. To properly choose the needed horsepower of a compressor, you must convert to SCFM.
It is important to understand that air is a compressible fluid. Conditions are dependent on location, time of year, altitude, etc. Because of these atmospheric variations (air pressure, temperature, and air density) the fluid properties of air are constantly changing. For example, conditions in Los Angeles, CA, USA, a location at sea level with an atmospheric pressure around 14.69 PSIA., will vary significantly to the conditions that exist in Denver, CO, USA, at an altitude of 5280 feet above sea level, and an atmospheric pressure of around 12.12 PSIA. For this reason, Dynabrade Inc. adheres to measuring maximum air flow in standard cubic feet per minute (SCFM).
NOTICE: ISO Standard: 68°F, 0% relative humidity, 14.5 PSIA (air pressure at sea level).
Formula to convert from SCFM to CFM:
SCFM x 14.7 / (Air Pressure in Pounds + 14.7) = CFM
Example: An orbital (59020) takes 14 SCFM to run. 14 (SCFM) x 14.7 / (90 + 14.7) = 1.96 CFM
To estimate CFM, use 7 as a conversion factor. This will not give an exact number, but it will come close to about what is needed. CFM to SCFM: CFM x 7 = SCFM SCFM to CFM: SCFM / 7 = CFM
Standard Cubic Feet per Minute (SCFM) will be a larger value than the CFM value. Why? CFM values are taken under pressure, usually 90 PSI, which accounts for the small air volume. SCFM is measured by expanding the air to a standard condition, taking into consideration the different variables such as temperature and pressure. Using the above formulas will help when figuring out the size air compressor is needed.
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