Soffit & Fascia Calculator
Estimate soffit panels and fascia board from the roof perimeter and overhang, with waste and an optional material cost.
How it works
fascia length = roof perimeter · soffit area = perimeter × (overhang ÷ 12) · both × (1 + waste%)
Fascia caps the ends of the rafters along the whole roof edge, so the fascia length is simply the perimeter of that edge. Soffit fills the underside of the overhang, a strip as wide as the overhang running the full perimeter, so its area is the perimeter times the overhang in feet. Both get a waste allowance for miter cuts at the corners and for the offcuts left when panels do not divide evenly into the run.
Worked example
A house with 140 ft of roof edge and a 16 in overhang: fascia = 140 ft, soffit = 140 × (16 ÷ 12) = 187 sq ft. Add 10% waste → 154 ft of fascia (about 13 twelve-foot boards) and 205 sq ft of soffit.
Frequently asked questions
How do I measure the roof perimeter for fascia?
Add up every eave and rake where the roof meets open air — the horizontal runs along the gutters plus the sloped runs up the gable ends. That total is the length of fascia you trim, and the run over which soffit is installed.
Vented or solid soffit?
Attics need intake ventilation, so at least part of the soffit should be vented panels to let air in under the roof. A common approach mixes vented and solid panels, or uses continuous vented soffit, to hit the required net free vent area.
Why include a waste factor?
Corners are mitered, panels rarely divide evenly into the run, and a few boards get cut short. Ten percent covers a straightforward roof; add more for many corners, gables and dormers.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.