Soffit and Fascia Calculator

Calculate the soffit panels and fascia boards needed to finish your roofline. Enter the house perimeter and profile dimensions for an instant material estimate.

What is Soffit and Fascia?

A soffit and fascia calculator determines the quantity of materials needed to finish the underside of roof overhangs (soffit) and the vertical board along the roof edge (fascia). These components serve both functional and aesthetic purposes: soffit provides ventilation to the attic while sealing out pests, and fascia protects the exposed rafter tails from weather while providing a mounting surface for gutters. Soffit is the finished underside of the roof overhang, spanning from the exterior wall to the fascia board. Standard soffit widths range from 6 inches (narrow eaves) to 24 inches (wide overhangs), with 12-16 inches being most common on residential homes. Soffit panels are typically sold in 12-foot lengths and come in the width of your overhang. Vented soffit panels have perforations that allow air to flow into the attic, which is essential for proper roof ventilation and preventing moisture buildup and ice dams. Fascia is the vertical trim board that caps the ends of the rafters along the roofline. It is the board directly behind the gutter. Standard fascia heights are 4-8 inches, corresponding to the rafter depth. Fascia is typically 3/4 to 1 inch thick and sold in 12-foot or 16-foot lengths. Materials include wood (cedar, pine, composite), aluminum (maintenance-free wrapping), and PVC (rot-proof). The calculation starts with the house perimeter, which represents the total linear run of soffit and fascia. For a rectangular house measuring 40x40 feet, the perimeter is 160 feet. Soffit area equals the perimeter multiplied by the soffit width (converted to feet). Soffit panels needed equals the total area divided by individual panel area (12 ft length times the soffit width). Fascia boards needed equals the perimeter divided by board length (typically 12 feet), rounded up. A waste factor of 10 percent covers material lost to cuts at corners, splices, and fitting around obstacles such as soffit vents, junction boxes, and architectural details. Homes with many inside and outside corners or complex rooflines may need 15 percent waste. The waste factor applies to both soffit and fascia quantities. When replacing soffit and fascia, inspect the underlying rafter tails and sub-fascia for rot before installing new material. Damaged structural members must be repaired first, or the new finish material will fail prematurely. Also verify that attic ventilation meets code requirements: most codes require 1 square foot of net free vent area per 150 square feet of attic floor space.

How to Calculate

1. Measure the perimeter of your house where soffit and fascia will be installed (in feet)
2. Measure the soffit width from the wall to the fascia (the overhang depth in inches)
3. Measure the fascia height (the depth of the fascia board in inches)
4. Set the waste factor (10% for simple rooflines, 15% for complex with many corners)
5. Review the soffit area, number of panels, fascia linear footage, and board count
6. When ordering, confirm panel width matches your overhang measurement

Formula

Soffit Width (ft) = Soffit Width (in) / 12 Soffit Area (sq ft) = Perimeter x Soffit Width (ft) x (1 + Waste Factor / 100) Soffit Panels = ceiling(Soffit Area / (12 ft x Soffit Width ft)) Fascia Linear Feet = Perimeter x (1 + Waste Factor / 100) Fascia Boards = ceiling(Fascia Linear Feet / 12) Panels are 12 ft long. Boards are 12 ft long. Ceiling function rounds up to whole units since partial panels/boards must be purchased as full pieces.

Example Calculation

A house with 160 ft perimeter, 12-inch soffit, 6-inch fascia, 10% waste: Soffit Width = 12 / 12 = 1 ft Soffit Area = 160 x 1 x 1.10 = 176 sq ft Panel Area = 12 x 1 = 12 sq ft per panel Soffit Panels = ceiling(176 / 12) = 15 panels Fascia Linear Feet = 160 x 1.10 = 176 ft Fascia Boards = ceiling(176 / 12) = 15 boards

Frequently Asked Questions