The Soffit Calculator turns your eave length and soffit depth into a material list: square feet of soffit, the number of 12 in × 12 ft panels with waste, sticks of J-channel and F-channel for the wall and fascia edges, fascia cover pieces, and the intake ventilation a fully vented soffit provides. Measure every eave run along the fascia, including porch and garage eaves, and measure depth from the fascia board to the wall. Multiply the two, divide by 12 square feet per panel and add 10% for cuts — 150 feet of eave at 16 inches deep is 200 square feet, or 19 panels. Channel runs along both edges of the soffit, so order roughly twice the eave length in 12 ft sticks. If you enter the attic floor area, the calculator also checks the intake side of balanced ventilation: at the 1/300 rule, half the required net free area belongs at the soffit, and vented vinyl soffit typically provides 5 to 10 square inches per square foot.
Soffit is bought by the panel and trimmed by the linear foot. Panels run from the wall to the fascia, so each 12 ft panel is cut into pieces as long as the soffit is deep, and the channel runs along both edges of every eave.
| Eave length | 12 in deep | 16 in deep | 24 in deep | J/F-channel sticks |
|---|---|---|---|---|
| 100 ft | 10 panels | 13 panels | 19 panels | 18 |
| 150 ft | 14 panels | 19 panels | 28 panels | 27 |
| 200 ft | 19 panels | 25 panels | 37 panels | 35 |
| 250 ft | 23 panels | 31 panels | 46 panels | 44 |
| 300 ft | 28 panels | 37 panels | 55 panels | 53 |
Deep soffits waste more: a 24 in soffit gets six pieces from a 12 ft panel, a 16 in soffit gets nine, a 12 in soffit twelve.
| Attic floor | Total NFA | Intake at soffit |
|---|---|---|
| 1,000 sq ft | 480 sq in | 240 sq in |
| 1,500 sq ft | 720 sq in | 360 sq in |
| 2,000 sq ft | 960 sq in | 480 sq in |
| 2,500 sq ft | 1200 sq in | 600 sq in |
Vented vinyl soffit is commonly rated around 5 to 10 square inches of net free area per square foot — the figure is printed on the carton. Insulation baffles must keep each rafter bay open or the vented soffit feeds nothing.
Multiply the total eave length by the soffit depth in feet to get square feet, divide by 12 square feet per standard vinyl panel and add 10% for cuts. A 150 ft eave run with a 16 in overhang is 200 sq ft, or 19 panels.
About twice the eave length, because channel runs along both the wall edge and the fascia edge. It comes in 12 ft sticks; add a stick or two for corners and returns.
Commonly 5 to 10 square inches of net free area per square foot, depending on the product — the rating is printed on the carton. Balanced ventilation puts half of the attic requirement at the soffit.
Across, from the wall to the fascia. Each panel is cut to the soffit depth and the offcuts are used on the next section.