Roof Ventilation CFM Calculator
Find out exactly how much attic ventilation your Tulsa-area home needs. Enter your attic square footage, roof pitch, and current vents — get required net free area per the 1/300 rule, CFM airflow, and how many ridge, soffit, or box vents to add. Built from IRC R806.2 ventilation requirements and Oklahoma climate data.
Ventilation CFM Calculator
Adjust the inputs — required net free area, CFM, and vents to add update instantly using the 1/300 ventilation rule.
How To Read Your Results
Net Free Area (NFA)
The 1/300 rule requires 1 sq ft of net free vent area for every 300 sq ft of attic floor — about 960 sq in for a 2,000 sq ft attic. NFA is the open area of a vent after screens and louvers, not its overall size. That's the number that matters for code and airflow.
CFM Airflow
Multiply your required NFA (in sq ft) by 750 ft/min — the standard design velocity for natural attic ventilation. A 2,000 sq ft attic needs about 5,000 CFM of airflow. Steeper pitches add attic volume, so the calculator adjusts your CFM target above 4/12.
Balance Intake & Exhaust
Ventilation only works when intake and exhaust are balanced — roughly 50/50. Soffit vents bring cool air in at the eaves; ridge and box vents let hot air escape at the peak. If you're short on either side, adding one type without the other won't fix the attic.
