Attic Ventilation Calculator
Calculate the required amount of ventilation to keep your attic cool and dry. Based on the 1:150 or 1:300 rule.
Most modern codes allow 1:300 if intake/exhaust is balanced.
Total NFA Needed
720 sq in
(5.0 sq ft)
Intake (Soffit)
360 sq in
50%
Exhaust (Roof)
360 sq in
50%
Vent Estimator
How many vents do I need? (Select vent NFA)
Need: 6 Soffit Vents
Need: 8 Box Vents
What is NFA?
Net Free Area (NFA) is the open area of a vent that allows air to pass through. It is usually stamped on the product. Proper attic ventilation extends roof life and reduces energy bills.
The 1/300 Rule
For every 300 square feet of attic floor space, you need 1 square foot of ventilation, split evenly between intake (soffit) and exhaust (ridge/roof) vents.