Roof Area Calculator
Estimate sloped roof surface area from building dimensions, overhang and pitch, then add waste and subtract large openings for a practical order area.
Default project preview
18.16 roofing squares
Plan footprint
1,472 ft²
Pitch factor
1.118
Sloped roof area
1,645.7 ft²
Net roof area
1,621.7 ft²
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Building length
Enter this project assumption in ft. The current imperial default is 44 ft.
Building width
Enter this project assumption in ft. The current imperial default is 30 ft.
Average overhang
Enter this project assumption in ft. The current imperial default is 1 ft. Minimum: 0.
Roof pitch rise
Enter this project assumption in per 12. The current imperial default is 6 per 12. Minimum: 0.
Large roof openings
Enter this project assumption in ft². The current imperial default is 24 ft². Minimum: 0.
Waste allowance
Enter this project assumption in %. The current imperial default is 12 %. Minimum: 0. Maximum: 50.
Material price per area
Enter this project assumption in per ft². The current imperial default is 2.75 per ft². Minimum: 0.
How to read the outputs
Plan footprint
including average overhang. Default preview: 1,472 ft².
Pitch factor
6-in-12 equivalent. Default preview: 1.118.
Sloped roof area
before opening deductions. Default preview: 1,645.7 ft².
Net roof area
after large openings. Default preview: 1,621.7 ft².
Waste allowance
cuts, laps and complexity. Default preview: 194.6 ft².
Material allowance
order area × entered price. Default preview: $4,994.98.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Plan area includes overhang on every side. Sloped area = plan area × √(12² + pitch rise²) ÷ 12. Subtract large openings, then multiply by the waste allowance.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Roof Area Calculator questions
Why is roof area larger than the building footprint?+
Roof slope increases the surface distance compared with the horizontal plan area, and overhang extends beyond the walls.
Should skylights be subtracted?+
Large openings can be deducted, but small openings may not reduce the order because flashing and cutting create extra waste.
Can complex roofs use this calculator?+
Measure each rectangular roof plane separately with its own dimensions and pitch, then add the resulting areas.