Enter the total eave length and the width of your overhang to see how much soffit material and J-channel to buy.
How to use the soffit calculator
- Add up every run of eave around the house and enter the total as one length.
- Enter the soffit width — the distance from the wall out to the fascia. This is usually 12, 16 or 24 inches.
- Add extra for the cuts at corners and gable returns.
- Enter your panel size to get a panel count, and a price for a cost estimate.
Formulas
Soffit area (ft²) = eave length (ft) × soffit width (ft) With extra = area × (1 + extra % ÷ 100) Panel area (ft²) = panel length (ft) × panel width (in) ÷ 12 Panels = area ÷ panel area, rounded up J-channel (ft) = eave length × 2
J-channel runs twice along every eave: once against the wall and once at the fascia, which is why the figure is double the eave length. Vented and solid panels are ordered in the same quantities; most installers run one vented panel in every three.
Worked example: 120 ft of eave with a 24 in overhang
- Soffit area: 120 ft × 2 ft = 240 ft².
- Add 10% for cuts: 240 × 1.10 = 264 ft².
- Panel area for a 12 ft × 16 in panel: 12 × 16 ÷ 12 = 16 ft².
- Panels: 264 ÷ 16 = 16.5, so 17 panels.
- J-channel: 120 × 2 = 240 ft.
Measuring the eave
Walk the house and measure each straight run of eave separately, then add them. Gable ends with a rake soffit count too, and their width is usually narrower than the eaves. If your overhang changes width around the house, run the calculator once per section and add the results rather than averaging.
Quick reference
| Eave length | 12 in overhang | 16 in overhang | 24 in overhang |
|---|---|---|---|
| 60 ft | 66 ft² | 88 ft² | 132 ft² |
| 100 ft | 110 ft² | 147 ft² | 220 ft² |
| 120 ft | 132 ft² | 176 ft² | 264 ft² |
| 160 ft | 176 ft² | 235 ft² | 352 ft² |
| 200 ft | 220 ft² | 293 ft² | 440 ft² |
Includes a 10% extra allowance.
Questions
How do I measure soffit?
Measure the total length of eave around the house, then the width from the wall to the fascia. Multiply the two for the square footage.
How many soffit panels do I need?
Divide the soffit area by the area of one panel. A 12 ft panel 16 in wide covers 16 ft², so 264 ft² of soffit takes 17 panels.
How much J-channel do I need for soffit?
Twice the eave length, because J-channel runs along the wall and along the fascia. 120 ft of eave takes about 240 ft.
How many vented soffit panels should I use?
A common approach is one vented panel in every three, but attic ventilation requirements depend on the attic area and the rest of the venting, so check your local code.
How do you calculate soffit square footage?
Multiply the total eave length by the overhang width in feet. 120 ft of eave with a 2 ft overhang is 240 ft²; add waste before dividing by the panel coverage.
Sources
- NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically, National Institute of Standards and Technology.
Used for: Exact inch, foot and gallon definitions and the metric conversions.