How do I calculate linear feet of soffit?

Linear feet of soffit equals the total length of all roof eaves where soffit will be installed. Walk around your home and measure each eave section with a tape measure, then add them together. For a simple rectangular home, it's roughly the perimeter of the house. Don't forget gable ends, dormers, and porch overhangs — each adds to the total linear footage.

What size soffit should I use?

Standard soffit overhang widths range from 12 to 24 inches, with 12 and 16 inches being most common. The size depends on your home's architectural style and climate. Wider overhangs (18–24 inches) provide more shade and rain protection but cost more. Check your existing soffit width — matching it is usually the simplest approach. Fascia boards typically come in 6, 8, or 10-inch widths.

How much does soffit installation cost per linear foot?

Soffit installation typically costs $6–12 per linear foot including materials and labor. Vinyl is the most affordable at $6–8/ft, aluminum at $8–10/ft, and wood or fiber cement at $10–12/ft. Labor alone averages $3–6 per square foot. For a typical 120-linear-foot home with 12-inch overhang, total installation costs range from $900–$1,800 depending on material choice and complexity.

Which soffit material is best for my climate?

For coastal or humid climates, aluminum is best — it won't rust, rot, or warp from moisture and salt air. For cold climates with freeze-thaw cycles, vinyl holds up well and doesn't require painting. For hot, dry climates, fiber cement offers excellent fire resistance and durability. Wood tongue-and-groove gives the best traditional appearance but requires the most maintenance in any climate.

Soffit Calculator

Total Eave Length

Soffit Width (Overhang)

Soffit Material

Fascia Material

Waste Factor

Attic Area

ft²

Ventilation Ratio

Vent NFA (sq in per vent)

Estimate Cost

Include soffit material and labor cost estimate

Vinyl Vented · 10% waste

Material Estimate

11panels

120 ft²11 fascia boards

Materials & Quantities

Material requirements including 10% waste factor

Soffit Area

120ft²

Soffit Panels

1110 panels without waste

Fascia Linear Feet

120ft

Fascia Boards

1112 ft boards · 10 without waste

Ventilation Requirements

Based on 1:150 rule with 50% intake split · 50 sq in NFA per vent

Physical Vents Needed

15for 1,500 ft² attic

Intake NFA Required

5sq ft

Waste Added

12ft²

What Is a Soffit Calculator?

Estimate soffit panels, fascia boards, and vent requirements for your home

A soffit calculator helps homeowners and contractors estimate how many soffit panels, fascia boards, and vent units are needed for a roofing project. Soffit is the material installed under the eaves (the roof overhang), while fascia is the vertical board that runs along the roof edge.

Material Types

12 ft²

Panel Coverage

$2–6

Per Sq Ft Installed

1:150

Vent Ratio

Proper soffit installation provides attic ventilation, prevents moisture buildup, keeps pests out, and gives your home a finished look. Getting the material estimate right saves money and avoids mid-project supply runs.

How Is Soffit Material Calculated?

The formula and methodology

The material calculation follows a straightforward area-based approach. You need two measurements: the total linear length of all eaves and the depth of the overhang (soffit width).

Measure Eaves

Eave Length = sum of all roof edges (ft)

Walk around the home and measure each eave section. Include gable ends, dormers, and porch overhangs.

Calculate Area

Soffit Area = Eave Length (ft) × Soffit Width (ft)

Soffit width in feet = overhang in inches ÷ 12. Standard overhangs are 12–24 inches.

Convert to Panels

Panels Needed = ⌈Soffit Area × (1 + Waste%) ÷ Panel Coverage⌉

Standard panels cover 12 sq ft. Always round up — soffit is sold in full panels only.

Example Calculation

For a home with 120 linear feet of eaves and a 12-inch overhang:

Soffit width in feet = 12 in ÷ 12 = 1 ft
Soffit area = 120 ft × 1 ft = 120 sq ft
With 10% waste = 120 × 1.10 = 132 sq ft
Standard vinyl panels (12 sq ft each) = 132 ÷ 12 = 11 → 11 panels

Fascia boards are calculated similarly: total eave length divided by the standard board length (typically 12 ft for aluminum/vinyl, 16 ft for wood), rounded up.

How Are Soffit Vents Calculated?

The 1:150 and 1:300 building code rules

Building codes (IRC 2021, Section R806) require attic ventilation based on attic floor area. The standard is 1 square foot of net free vent area per 150 square feet of attic space (1:150 rule). The 1:300 exception applies only when a vapor retarder is installed and ventilation is evenly split between upper and lower portions of the attic.

Ventilation is split 50/50 between intake (soffit vents) and exhaust (ridge/roof vents). So the number of soffit vents equals half the total vent area requirement.

Determine Attic Area

Attic Area = length × width of attic floor (sq ft)

Measure the attic floor, not the roof surface. Include the entire conditioned footprint.

Apply Vent Ratio

Total NFA = Attic Area (sq ft) ÷ Ratio (150 or 300)

NFA = Net Free Area. Use 1:150 for most climates, 1:300 where code permits less ventilation.

Split & Count Vents

Soffit Vents = ⌈Total NFA (sq in) ÷ Vent NFA ÷ 2⌉

50% intake (soffit) / 50% exhaust (ridge). Standard soffit vents provide ~50 sq in of NFA each.

Example (1:150 rule, 1,500 sq ft attic)

Total vent area needed = 1,500 ÷ 150 = 10 sq ft
Soffit intake share = 10 ÷ 2 = 5 sq ft (720 sq in)
With 50 sq in vents = 720 ÷ 50 = 15 vents (round up)

Material Options Comparison

Vinyl, aluminum, wood, and fiber cement compared

Vinyl$2–4/sq ft

+ Low maintenance, won't rot, affordable

− Can crack in extreme cold, fades over time

Aluminum$3–5/sq ft

+ Rust-proof, fire-resistant, ideal for coastal climates

− Can dent from impact, limited color options

Wood (T&G)$3–6/sq ft

+ Classic natural look, can be stained any color

− Requires repainting every 3–5 years, vulnerable to rot

Fiber Cement$3–5/sq ft

+ 30–50 year lifespan, fireproof, pest-resistant

− Heavier than other options, requires special cutting tools

Common Mistakes to Avoid

Avoid these pitfalls for an accurate soffit estimate

Not accounting for waste

Always add 10–15% extra for cuts, mistakes, and complex corners. Running short mid-project delays work and may result in mismatched dye lots.

Using the wrong vent ratio

The 1:150 rule applies in most climates. Check your local building code — some jurisdictions require the stricter 1:150 ratio.

Mixing vented and solid soffit incorrectly

If using vented soffit for intake air, ensure the attic has adequate exhaust ventilation (ridge vents, gable vents). Intake without exhaust doesn't work.

Forgetting fascia trim and accessories

F-Channel (at the wall) and J-Channel (at the fascia) are required for most installations. Our calculator focuses on panels and boards — order trim separately.

Frequently Asked Questions

Common questions about soffit materials, vents, and installation

Measure the total linear feet of all eaves (the roof overhang edges). Then measure the soffit width (the overhang depth from the exterior wall to the fascia board) in inches and convert to feet by dividing by 12. Multiply eave length × soffit width to get the total square footage. Add 10–15% for waste, then divide by the panel coverage (standard panels cover 12 sq ft each). Round up to the nearest whole panel.

Per the IRC building code (1:150 rule), you need 1 square foot of net free vent area for every 150 square feet of attic space. This is split 50/50 between intake (soffit) and exhaust (ridge/roof). So divide your attic square footage by 150, then divide by 2 for the soffit share. Convert to square inches (× 144) and divide by the net free area of your chosen vent (typically 50 sq in per vent). Our calculator does this automatically.

The 1:150 rule is a building code requirement (IRC Section R806) that mandates 1 square foot of net free ventilation area for every 150 square feet of attic floor space. This ensures adequate airflow to prevent moisture buildup, ice dams, and premature roof deterioration. The 1:300 exception is only allowed when a vapor retarder is installed on the warm side of the ceiling and ventilation is evenly distributed between the upper and lower portions of the attic space.

Vented soffit panels have perforations or built-in vents that allow air to flow into the attic space, providing intake ventilation. Solid (non-vented) soffit is a continuous panel with no openings. Vented soffit is used when the attic needs airflow — it works with ridge or roof vents to create natural convection. Solid soffit is used in enclosed porch ceilings, carports, or when ventilation is provided elsewhere.

Calculate total ventilation needed: attic square footage ÷ 150 (or 300) = square feet of net free area (NFA). The soffit share is 50% of this total. To find the number of vents: convert the soffit NFA to square inches (× 144), then divide by the NFA rating of one vent. Example: 1,500 sq ft attic ÷ 150 = 10 sq ft total NFA. Soffit share = 5 sq ft = 720 sq in. With 50 sq in vents, you need 720 ÷ 50 = 15 vents.

Yes, both are typically needed. F-channel is mounted on the exterior wall to receive the inner edge of the soffit panel. J-channel is installed along the fascia board to receive the outer edge. These trim pieces hold the soffit panels in place and give a clean, finished look. Our calculator estimates panels and fascia boards — remember to order F-channel and J-channel trim separately based on your total eave length.

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Last updated May 28, 2026