Soffit Calculator
Calculate total soffit surface area needed under a roof eave overhang based on perimeter length and width.
Calculation Results
The total required surface area of soffit panels including waste.
How This Calculator Works
To use the Soffit Calculator:
- Enter the total roof perimeter running length where soffit panels will be placed.
- Enter the horizontal width of your soffits (common residential overhang widths are 12 inches, 18 inches, or 24 inches).
- Specify a waste allowance (10% is standard to cover cutoffs, corners, and joints).
- The calculator immediately displays the total square footage of soffit material you need to order.
Formula & Calculations
To estimate soffit material needs, we calculate the surface area of the underside of the roof eaves. We multiply the roof perimeter running length by the soffit width (overhang):
Base Soffit Area = Perimeter × Soffit Width
We then apply the waste factor to find the final adjusted square footage needed to purchase:
Total Soffit Area = Base Soffit Area × (1 + Waste / 100)
Step-by-Step Calculation Examples
Standard Home Eaves
Calculating soffit area for a 120-foot run with an 18-inch (1.5 ft) eave overhang and a 10% waste buffer.
- perimeter: 120
- soffit_width: 18
- waste: 10
- total_soffit_area: 198.0 sq ft
Deep Overhang Custom Home
Calculating soffit area for a 180-foot run with a deep 24-inch (2.0 ft) overhang and a 12% waste buffer.
- perimeter: 180
- soffit_width: 24
- waste: 12
- total_soffit_area: 403.2 sq ft
Frequently Asked Questions
What is a soffit?
The soffit is the exposed undercard beneath the overhanging section of a roof eave. It covers the rafters and is typically vented to allow cool air to flow into the attic space.
What is the standard width for soffits?
Standard residential soffit widths are typically 12 inches or 18 inches, although 24-inch overhangs are also very common on custom designs and high-wind structures.
What materials are soffit panels made of?
Soffits are commonly made from vinyl (durable and maintenance-free), aluminum (lightweight and paintable), fiber cement, or natural cedar wood.
Why do soffits need to be vented?
Vented soffit panels allow fresh, dry air to enter the attic floor space. This intake air sweeps hot, damp air out through the ridge vents at the top of the roof, preventing moisture and heat buildup.
How do I calculate soffit panel count from area?
Divide the total soffit area by the square footage of a single soffit panel. For example, a common 12-foot vinyl soffit panel that is 1 foot wide covers 12 square feet. If you need 198 sq ft of soffit, you would buy 17 panels.