Roof Vent Calculator
Estimate attic net-free ventilation area, intake and exhaust vent quantities, installed capacity and material cost from attic floor area.
Default project preview
720 in² NFA
Exhaust vents
6
Intake vents
40
Exhaust capacity
360 in²
Intake capacity
360 in²
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Required NFA = attic floor area ÷ ventilation ratio, converted to square inches or square centimetres. Intake and exhaust quantities round up from their assigned shares.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Roof Vent Calculator questions
What is net free area?+
Net free area is the open airflow area after screens, louvers and vent construction reduce the gross opening.
Why balance intake and exhaust?+
Balanced low intake and high exhaust helps ventilation operate without starving one side of the airflow path.
Is a 1:300 ratio always allowed?+
No. The applicable ratio depends on the assembly, vapor control and local requirements.