Roofing calculator
Roofing calculator
Calculate roof area, waste-adjusted area, and estimated material quantity for flat, gable, and shed roofs.
What it does
- Finds the actual roof surface area
- Adds a waste factor for ordering
- Gives a material quantity estimate in m2
A simple gable roof example you can check at a glance
Example build-up
Length: 12 m, width: 8 m, pitch: 30 degrees, waste: 12 percent.
Roof area = 110.9 m2. Adjusted area with waste = 124.2 m2. Use that figure as the area-based material estimate.
Formula
Area = length × width ÷ cos(pitch)
Adjusted area = area × (1 + waste / 100)
Enter the roof dimensions
Area-based estimate for roofing products.
For gable and shed roofs, the pitch increases the roof surface. Flat roofs ignore the pitch field.
What each input means
Roof type
Choose flat for a level roof, gable for two-sided slopes, or shed for a single-pitch roof.
Pitch and waste
Pitch converts plan area into slope area. Waste adds ordering allowance for cuts, overlaps, and trimming.
Material quantity
Use the adjusted area as a practical estimate for area-based roofing materials. Check the pack coverage before ordering.
Detailed roofing notes and example pages
Pitched roof guide
How pitch changes the area and why the slope factor matters for ordering.
Open guideRoof waste guide
Choosing a realistic waste percentage for membranes, boards, tiles, and sheets.
Open guideConcrete volume calculator
Switch to a related construction-quantity calculator for slabs, footings, and columns.
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