Soffit & Fascia Calculator — How Much Soffit and Fascia Do I Need?
Calculate the linear feet of fascia board and square feet of soffit needed for your roof overhang. Includes J-channel and panel counts.
How to Use This Calculator
- Enter your building length and width
- Measure or estimate the overhang depth (distance from wall to fascia board)
- Select roof style — gable roofs have rake overhangs on the two end walls
- Click Calculate to get fascia linear feet, soffit sq ft, panels, and J-channel
How the Calculation Works
fascia_linear_ft = building_perimeter (all 4 sides)
// Gable roofs add rake overhang on 2 short ends:
fascia_gable_ft = perimeter + 2 × building_width
soffit_sqft = perimeter × (overhang_depth_in / 12)
soffit_panels = ⌈soffit_sqft / 12⌉ // 12"×12ft panel = 12 sqft
// J-channel (top + bottom edge of soffit):
j_channel_ft = perimeter × 2
fascia_boards_12ft = ⌈fascia_linear_ft / 12⌉ Fascia board runs along the lower edge of all rafters and covers the rafter tails — total linear feet equals the roof perimeter. Soffit fills the horizontal gap between the fascia and the wall. Soffit square footage is the perimeter multiplied by the overhang depth.
Variables:
- building_perimeter: Total perimeter of the building (2 × length + 2 × width)
- overhang_depth_in: Width of the roof overhang / soffit in inches
Pro Tips
- Fascia runs along the entire perimeter of the roof — measure all four sides
- Soffit depth is the width of the overhang from the wall face to the fascia board
- Vented soffit allows attic airflow — required by code in most jurisdictions
- Add 10% waste for cuts around corners and end treatments
- Fiber cement and vinyl soffit/fascia require less maintenance than painted wood
Recommended Products
Gentek 12" Vented Aluminum Soffit — 12 ft
1/3 vented aluminum soffit panel for attic airflow.
View on Amazon →Ply Gem 5/4x6 PVC Fascia Board — 16 ft
Cellular PVC fascia — rot-proof, paintable, low maintenance.
View on Amazon →Prime Source J-Channel Aluminum — 10 ft
Aluminum J-channel for finishing soffit edges.
View on Amazon →Coil Roofing Nails 1-1/4" Galvanized — 1 lb
Ring-shank nails for soffit and fascia attachment.
View on Amazon →Frequently Asked Questions
How wide should a roof overhang be?
Standard overhangs are 12–24 inches. Wider overhangs provide better protection from rain and sun. Code minimum is typically 12 inches in most climates.
What is the difference between soffit and fascia?
Fascia is the vertical board at the end of the rafters where gutters attach. Soffit is the horizontal surface underneath the overhang, connecting the fascia to the building wall.
Should I use vented or solid soffit?
Vented soffit is recommended in most applications as it allows air to flow into the attic, preventing moisture and heat buildup. Solid soffit is only used with other ventilation methods.
How is soffit sold?
Vinyl soffit is sold in 12-inch wide panels in 12-foot lengths (12 sq ft per panel). Measure your soffit area in square feet and divide by 12 to get the number of panels needed.