Soffit Calculator
Calculate the soffit area under your roof's eaves from the roofline perimeter and overhang width, for material ordering.
How this calculator works
Soffit is sold and installed by area, so ordering the right amount starts with knowing how much horizontal surface sits under your eaves. This calculator takes your eave perimeter and your overhang width, converts the width from inches to feet, and multiplies the two to give you the total soffit area.
Formula: Soffit area = eave perimeter × (overhang width in inches ÷ 12).
Worked example
A 140 ft eave perimeter with an 18-inch overhang:
- Overhang in feet: 18 ÷ 12 = 1.5 ft
- Soffit area: 140 × 1.5 = 210 sq ft
Notes
Soffit only covers the horizontal underside of the roof overhang — it doesn’t include the fascia, the vertical board running along the edge of the roofline. Fascia is a separate item, usually measured and priced along the same perimeter length but ordered on its own even though the two are installed together.
Venting requirements don’t change the area figure. Whether you go with continuous soffit vent panels or individual vents cut into solid panels, the square footage needed to cover the overhang stays the same — the vent choice only affects which panel product you buy.
How to use
Measure your home’s eave perimeter and the width of the overhang in inches, then enter both figures. The calculator converts the overhang to feet and returns the total soffit area you need to order.
A material planning estimate. Measure your actual eave perimeter and overhang for a precise order, and add extra for waste on cuts.
Frequently asked questions
What is soffit, and where is it on my house?
Soffit is the material covering the horizontal underside of your roof's overhang — the section you'd see looking straight up if you stood underneath the eave. It's distinct from fascia, which is the vertical board running along the edge of the roofline.
How do I measure my eave perimeter?
Walk the full outline of your roof's edge where the overhang exists and add up each straight section's length. This is the same perimeter measurement most roofers use for fascia and gutter runs, so if you already have that figure you can reuse it here.
Does the overhang width need to be the same all around the house?
This calculator assumes one consistent overhang width applied to your full eave perimeter. If your overhangs vary significantly by side, it's more accurate to calculate each side separately with its own width and add the areas together.
Do I need extra soffit for vents?
Vent choice — continuous soffit vent strips versus individual round or rectangular vents — changes which panel type you buy, not the total area you need to cover. Calculate area the same way either way, then check your chosen product's spacing requirements for vent placement.
Estimates only. Verify quantities with your supplier before purchasing.