ANYCALCULATOR     ATTIC VENTILATION CALCULATOR Note: Calculations are based on 1 square foot of Net Free Area for every 150 square feet of atic floor space. Select the roof pitch that is closest to yours: ROOF PITCH :   Up to 6/12     7/12 to 10/12     11/12 and Up To Determine Roof Pitch : Place a level against the roof. From the point where the level touches the roof, measure out 12 inches. From this point measure the distance in inches from the bottom of the level to the roof. This will be the first number in the roof pitch. the second number will always be 12. Enter the width and length of your house, including overhang (in feet):  WIDTH :   Ft   LENGTH :   Ft   ATTIC SIZE :   Sq. Ft.   Read Intake Vents and Exhaust Vents needed at specific Roof Pitch. Numbers are expressed as Linear Feet. 9 sq.in./foot NFA Continuous Soffit Intake Vents Linear Ft.  You need  8' pieces  or   12' pieces For attics greater than 3500 sq.ft. we recommend a minimum of 12.7 NFA per foot WIDE / HAT SHAPED VENT WIDE - 12.7 sq.in./foot NFA Linear Ft. You need  8' pieces 12.7 sq.in./foot NFA Continuous Soffit Intake Vents for 0 lot line RIDGE VENTS (EXHAUST) - 18 sq.in./foot NFA Ridge Vents with Baffle System Linear Ft. We recommend running ridge vent and soffit vents continuously in all available horizontal areas for best air flow.