Linear feet, soffit sq ft & fascia boards
Soffit and fascia are the two trim elements that finish the edge of a roof where it meets the walls. The fascia is the horizontal board (or aluminum coil wrap) running along the rafter tails, and the soffit is the material covering the underside of the eave overhang. Together they close off the attic, support gutter systems, and give the roofline a clean finished edge. This calculator turns a handful of simple site measurements into a complete material list so you can order coil stock, panels, or lumber with confidence.
Measurements can come from two directions. If you are working from plans, enter the building footprint length and width and the calculator derives the eave perimeter using the standard rectangular formula P = 2(L + W). If you already walked the house with a tape, enter the measured eave perimeter directly instead. You then supply the overhang width (the horizontal distance from the wall to the fascia, typically 12 to 24 inches) and indicate how many sides actually have open eaves — gable ends usually have no soffit unless they have an overhang with rakes.
The results include total fascia linear feet, total soffit area in square feet, the number of fascia boards needed at your chosen board length, and a cost estimate based on the unit prices you enter. Because prices for aluminum coil, vinyl panels, and wood vary by region and supplier, the calculator leaves pricing fully under your control rather than assuming a number that may be stale or wrong for your market.
The math behind the tool is deliberately transparent. Fascia length equals the eave perimeter along the sides that have open eaves. Soffit area equals that same perimeter multiplied by the overhang width, converted to feet: soffit area (sq ft) = perimeter (ft) × overhang (in) ÷ 12. Fascia board count divides total linear feet by the usable board length and rounds up, which is where the classic ordering mistake happens — forgetting that each cut leaves an offcut that is often unusable.
For a rectangular footprint of 40 ft × 28 ft with a 16-inch overhang on all four sides, the perimeter is 2 × (40 + 28) = 136 ft. Soffit area is 136 × 16 ÷ 12 ≈ 181 sq ft. At 16-ft boards you would need 136 ÷ 16 = 8.5, rounded up to 9 fascia boards before waste. Adding a 10 percent cutting allowance is the usual practice for straightforward runs and more for houses with many corners, bays, or returns.
The three dominant soffit and fascia material families each trade cost against maintenance. Wood is the traditional choice: inexpensive and paintable, but it needs repainting every few years and can rot where moisture sits. Aluminum coil stock wrapped over wood fascia is close to maintenance-free and is what most seamless-gutter crews install, since the same brake that forms gutter also forms coil. Vinyl soffit panels are the most common soffit product in new residential construction — they come in solid, center-vent, and fully vented profiles that snap together and never need paint.
Ventilated soffit is not just a finish choice; it is part of the attic ventilation system. Continuous soffit venting works with ridge vents to drive passive airflow, which most building codes address through net free venting area requirements — commonly calculated as 1 square foot of net free vent area per 150 square feet of attic floor space, or per 300 when a balanced system with both low and high vents is used. If you are replacing solid soffit with vented panels, it is worth checking that the attic has a matching exit path at the ridge or through static vents.
| Material | Typical form | Relative cost | Maintenance | Notes |
|---|---|---|---|---|
| Wood | 1× fascia boards, plywood soffit | Low | Repaint every few years | Paintable, traditional look |
| Aluminum coil | Formed on site over wood | Medium | Essentially none | Installed with seamless gutters |
| Vinyl | Interlocking soffit panels | Medium | None | Solid, center-vent, or fully vented |
| Fiber cement | Boards and panels | Higher | Repaint far less often | Fire resistant, used on premium builds |
A few field practices make the estimate much more reliable. Measure the overhang at several points, not just one — older homes frequently have overhangs that drift an inch or two from corner to corner. Count outside and inside corners separately if you are ordering coil stock or corner trim, because corners consume more material than their linear length suggests. Finally, keep the quote you receive itemized by linear foot and square foot so you can audit it against this calculator line by line.
How do I measure the eave perimeter for fascia?
Measure along the fascia line at each side of the house that has an open eave and add the runs together. For a simple rectangle you can also use the footprint: perimeter = 2 × (length + width). Exclude gable ends unless they also have horizontal rakes trimmed in fascia.
How is soffit square footage calculated?
Soffit area = eave perimeter (feet) × overhang width (inches) ÷ 12. For example, 120 ft of perimeter with an 18-inch overhang gives 120 × 18 ÷ 12 = 180 sq ft of soffit.
How many 16-foot fascia boards do I need?
Divide total fascia linear feet by the board length and round up, then add waste. 100 linear feet at 16-ft boards is 100 ÷ 16 = 6.25, so 7 boards — plus about 10% extra for cuts and defects on simple runs.
Should soffit be vented or solid?
Vented soffit feeds fresh air into the attic, pairing with ridge or static vents for passive ventilation. If the attic already has adequate intake elsewhere, solid or center-vent panels are fine; many crews mix vented panels into runs closest to the eave edge.
Does this work for aluminum coil and vinyl too?
Yes. Linear feet of fascia drives coil stock, and square feet of soffit drives panel or plywood quantities regardless of material — just enter the unit prices for the product you are actually buying.