to get the CFM you take the crosssectional area ( length x width ) of the rectangular duct or pi x r^2 for round and multiply by the velocity ..example,,,,vel= 2 m/sec.. ,,,,,,50
http://answers.yahoo.com/question/index?qid=200907...

1. Measure the length and width of a room where you need to calculate the required airflow. Multiply these together to get the square footage of the room, i.e. if the room is 10 ft
http://www.ehow.com/how_5677999_calculatecfmhvac...

Cubic Ft / Min.
http://wiki.answers.com/Q/What_is_CFM_in_HVAC_syst...

This is the formula for fan CFM: Cubic feet per minute: air speed (feet per minute) X area
http://www.chacha.com/question/whatisthecfmfor...
