Finish · Project tools
Siding & exterior coverage calculator
Add wall faces and triangular gables, subtract usable openings, and estimate the coverage to order.
Measure your project
Add separate sections for irregular spaces. Avoid overlaps. Use 10.5 ft for 10 ft 6 in.
Match your material
Use your plan, product label or supplier’s specifications.
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Understand the number
How this estimate works
Rectangle area = length × height. Triangle area = base × height ÷ 2. Add the faces, subtract the specified openings and apply your allowance. Divide by installed package coverage and round up.
Separate rectangles from gables
Measure each wall face and add gables as triangles, using the triangle’s own height. Do not count the rectangle below a gable twice. Openings can reduce surface area, but a window cutout does not always produce a reusable piece. Keep waste and deductions consistent with the contractor’s intended layout.
Coverage is different from board size
Lap siding covers less than its full board width because courses overlap. Use the manufacturer’s installed exposure or package coverage. Trim, starter pieces, corners, joints, soffit, fascia and weather-resistive layers are separate parts of the quote. The calculator does not specify attachment or wind-load details for a coastal property.
Before you request a quote
- Each wall face measured once
- Gables added separately
- Installed exposure confirmed
- Trim and corners counted
- Attachment and weather barrier specified
Product guidance and further reading
Published by Gulf Coast Project Pros · September 15, 2026. Calculations use your inputs; product suitability and project requirements must be checked separately. Report a correction.