have to multiply the brake horsepower at standard conditions by the air density correction factor. Air Movement and Control Association fan rating The centrifugal fan performance tables provide the fan revolutions per minute (RPM) and brake horsepower requirements for the given CFM and static pressure at standard air density (0.075 pounds per cubic foot). When the centrifugal fan performance is not at standard conditions, the performance must be converted to standard conditions before entering the performance tables. Centrifugal fans rated by the Air Movement and Control Association (AMCA) are tested in laboratories with test setups that simulate installations that are typical for that type of fan. Usually they are tested and rated as one of four standard installation types as designated in AMCA Standard 210. AMCA Standard 210 defines uniform methods for conducting laboratory tests on housed fans to determine airflow rate, pressure, electric power and energy efficiency, at a given speed of rotation. The purpose of AMCA Standard 210 is to define exact procedures and conditions of fan testing so that ratings provided by various manufacturers are on the same basis and may be compared. For this reason, fans must be rated in SCFM. See also Cubic feet per minute (CFM) Standard cubic feet per minute (SCFM) Standard cubic foot (SCF) Million standard cubic feet per day (MMSCFD) Gas compressor Centrifugal fan Combined gas law References External links Xchanger Inc, webpage Calculator for SCFM, NM3/hr, lb/hr, kg/hr, ACFM & M3/hr gas flows. ACFM versus SCFM for ASME AG-1 HEPA Filters SCFM versus ACFM SCFM versus ACFM What is SCFM? SCFM, ACFM, ICFM...What Does it Mean? What is the difference between ACFM and SCFM? SCFM (Standard CFM) vs. ACFM (Actual CFM) SCFM vs ACFM Gas Density Properties of Atmosphere ACFM versus SCFM versus ICFM Temperature and Altitude Affect Fan Selection ACFM to SCFM vs ICFM Calculations SCFM VS ACFM Good write up on the math Units of flow