🏠 Soffit Calculator
Panels, channel, fascia and intake vent area from your eave length
Smart Roofing Calculator — Soffit Calculator — smartroofingcalculator.com/soffit-calculator/ — printed
Fascia to wall
12 in × 12 ft vinyl = 12
Printed on the carton
📏 Measure every eave run along the fascia, including porch and garage eaves.
🛠️ How This Calculator Works
Enter the total length of every eave and the soffit depth. The calculator converts that to square feet, divides by panel coverage with waste, counts channel for both edges of the soffit, and checks the intake vent area against your attic.
📐 Formula
Panels = ⌈Eave ft × (Depth in ÷ 12) × (1 + Waste%) ÷ Panel sq ft⌉ · Channel = Eave × 2 · Intake needed = Attic ÷ 150 (÷ 300 only under the IRC R806.2 exception) × 144 ÷ 2📝 Example Calculation
150 ft of eave, 16 in deep, 10% waste: • Area 200 sq ft → 220 with waste → 19 panels • Channel: 300 ft → 27 twelve-foot sticks • Vented at 6 sq in/sq ft: 1,200 sq in of intake
💡 Pro Tips from Roofers
- Leave 1/4 in at each channel for expansion — vinyl moves.
- Nail in the centre of the slot, never tight.
- Keep insulation baffles in every rafter bay so the vented soffit actually feeds the attic.
- Use solid soffit over porches and heated rooms with no attic above.
❓ Frequently Asked Questions
How do I calculate how much soffit I need?
Multiply the total eave length by the soffit depth in feet to get square feet, then divide by the coverage of one panel (12 sq ft for a standard 12 in × 12 ft vinyl panel) and add 10% for cuts. A 150 ft eave run with a 16 in overhang is 200 sq ft, or 19 panels with waste.
How much J-channel and F-channel do I need for soffit?
You need one run of channel along the wall and one along the fascia for every foot of eave, so roughly twice the eave length. Channel comes in 12 ft sticks; add a stick or two for corners and returns.
How much intake ventilation does vented soffit give?
It depends on the product — vented vinyl soffit is commonly rated around 5 to 10 square inches of net free area per square foot, and the figure is printed on the carton. Balanced ventilation puts half of the attic's required net free area at the soffit.
Should soffit panels run across or along the eave?
Across. Panels run from the wall to the fascia, perpendicular to the eave, so each panel's length is cut down to the soffit depth and the offcuts are used on the next section.
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How much soffit do I need?
Multiply the total eave length by the soffit depth in feet, divide by 12 sq ft per panel and add 10%. Panels run from the wall to the fascia, so every panel is cut down to the soffit depth and the offcut is used on the next bay. Deep soffits waste more: a 24 in soffit gets six pieces out of a 12 ft panel, a 16 in soffit gets nine.
Soffit panels by eave length and depth
| Eave length | 12 in deep | 16 in deep | 24 in deep | 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 |
12 in × 12 ft panels, 10% waste. Channel covers the wall edge and the fascia edge, plus 5%.
Soffit vents: how much intake is enough?
Balanced attic ventilation puts half of the required net free area (NFA) at the soffit and half at the ridge. At the IRC R806.2 default of 1/150 an attic of 1,500 sq ft needs 10 sq ft (1,440 sq in) of NFA in total, so 720 sq in of intake (half that only where the 1/300 exception applies: balanced vents, plus a vapor retarder in climate zones 6–8). Vented vinyl soffit is commonly rated around 5–10 sq in of NFA per square foot — check the carton — so 150 ft of 16 in soffit fully vented provides roughly 1,000–2,000 sq in, enough for that attic. Intake is only real if insulation baffles keep each rafter bay open. Size the exhaust side with the ridge vent calculator.
Siding the walls as well? The siding calculator gives squares, vinyl cartons and starter strip.
Having it installed? The soffit replacement cost calculator prices soffit and fascia with labour, staging and overhead.
Adding intake vents to an existing soffit? The roof vent installation cost calculator prices a soffit vent job at $315–$465.
🔗 Related Roofing Calculators
- Soffit & Fascia Cost Calculator — Installed price per linear foot with labor
- Ridge Vent Calculator — Size the exhaust to match your soffit intake
- Roof Vent Calculator — Total intake and exhaust NFA for your attic
- Roof Overhang Calculator — Set the eave depth before ordering soffit
· Reviewed by the Smart Roofing Calculator editorial team