How to use the soffit and fascia calculator
- List each roof edge with a name, its length in feet and the soffit depth, the distance the overhang reaches from the wall.
- Add as many edges as you need, such as the front, the back and any gables with an overhang.
- Open More options to add a waste share, the length of fascia boards and the coverage of a soffit panel.
- Read the fascia in linear feet, the soffit in square feet and the boards and panels to buy.
Formula
fascia = sum of the edge lengths
soffit area = sum of (edge length x soffit depth)
with waste, multiply both by (1 + waste / 100)
boards = fascia / board length, rounded up; panels = soffit area / panel coverage, rounded up
Fascia runs along the length of an edge, so each edge adds its length. Soffit is a flat strip under the overhang, so each edge adds its length times its depth.
Two 60 foot eaves with 2 foot soffits
Two 60 foot eaves with a 2 foot soffit each need 60 + 60 = 120 feet of fascia and 60 x 2 + 60 x 2 = 240 square feet of soffit. With 10 percent waste, that becomes 132 feet of fascia, which is 11 boards of 12 feet, and 264 square feet of soffit, which is 9 panels of 32 square feet.
A house with edges of 40 feet, 25 feet, 40 feet and 25 feet and a 1.5 foot soffit needs 130 feet of fascia and 195 square feet of soffit.
Measuring each edge
Measure along the edge of the roof where the fascia will be mounted. Roof edges that slope, called rakes, are longer than their horizontal run, so measure the true length along the slope. The soffit depth is the distance from the wall to the outer edge of the overhang, measured flat.
Pieces come in set lengths and need joints, so the board count is a minimum. Corners, returns and splices can use more material than the bare total.
Trim and other roof planning
Gutters mount on the fascia, so size them with the Gutter and Downspout Calculator. For the roof itself, use the Roofing Calculator, and compare wall coverings with the Siding Calculator.
Assumptions and limits
- Soffit is a flat rectangle under each edge.
- Vented panels, J-channel, trim pieces and corner returns are not counted.
- One waste share is applied to fascia and soffit alike.
- Rake edges must be entered at their true sloped length.
Frequently asked questions
How much soffit do I need?
Multiply the length of each overhang by its depth and add them up. Two 60 foot eaves with 2 foot soffits need 240 square feet.
How is fascia measured?
In linear feet along the roof edge. It equals the total length of the edges that get a fascia board.
How many fascia boards do I need?
Divide the linear feet by the board length and round up. With 132 feet and 12 foot boards that is 11 boards, though joints and corners can use more.
Should I add waste?
Many installers add some for cuts and mistakes. Enter a waste percent in More options and both totals rise by that share.