Roof square footage calculator
Published On: 05/03/2026
Roof Square Footage Calculator
Estimate your roof’s total square footage (sloped surface area) from building dimensions and roof pitch. Includes an optional waste factor and converts to roofing squares (100 ft²).
Inputs explained:
• Length and Width: building footprint (outside-to-outside).
• Roof pitch: slope ratio (e.g., 4/12). A steeper roof has more surface area than a flat footprint.
• Overhang (optional): added to both sides of length and width to reflect eaves.
• Waste factor: extra % for cuts, starter strips, hips/valleys, and mistakes (often 10–15%).
• Length and Width: building footprint (outside-to-outside).
• Roof pitch: slope ratio (e.g., 4/12). A steeper roof has more surface area than a flat footprint.
• Overhang (optional): added to both sides of length and width to reflect eaves.
• Waste factor: extra % for cuts, starter strips, hips/valleys, and mistakes (often 10–15%).
Added to length & width on both sides.
Optional multiplier for hips/valleys/dormers.
Roof Square Footage Calculator — Description
The Roof Square Footage Calculator estimates the total surface area of your roof (in square feet) based on building footprint dimensions and roof pitch. Since a sloped roof has more surface area than a flat footprint, the calculator applies a pitch multiplier and optional complexity and waste factors. It also converts the result into roofing squares (1 square = 100 ft²) for easy material planning.
Use this tool to estimate roof area before ordering shingles, underlayment, and other roofing materials.