Estimate developed roof area, roofing squares and optional bundles or sheets from building dimensions, overhangs, pitch and waste.
Roof material calculator
Convert building footprint and pitch into developed roof area, then add overhangs, waste, bundles, sheets and pricing.
Measure the finished project dimensions and confirm product coverage on the manufacturer label before ordering.
Project estimate
Enter your measured dimensions and product details, then calculate the project estimate.
Methodology
The horizontal plan area includes the entered overhang at both ends and sides. It is multiplied by √(1 + (pitch rise ÷ 12)²) to obtain the developed area for a uniform slope. Waste is then added. Optional bundle and sheet counts divide by the exact coverage you provide and round up.
Worked example
A 40 ft by 30 ft footprint with no overhang and a 6:12 pitch has a slope factor of about 1.118. Its developed roof area is about 1,342 ft² before waste, or 13.42 roofing squares.
Roof measurement guide
First calculate the developed roof area from the footprint and pitch. Then use the manufacturer’s installed coverage for shingles, panels or sheathing, because nominal package dimensions can differ from effective coverage.
Formula reference
Related project tools
Common questions
The horizontal footprint is multiplied by the slope factor √(1 + (rise/run)²). This calculator expresses run as 12, so a 6:12 pitch uses 6 ÷ 12.
A roofing square is 100 square feet of roof area. It is an area unit, not the same as one bundle of shingles.
Bundle coverage varies by product and sometimes by application. Enter the installed square-metre coverage shown by the manufacturer instead of assuming a fixed bundle count.
Yes. Enter the horizontal overhang at each end and each side. The calculator adds both sides before applying the pitch factor.
Use it only as a first estimate for a uniform-pitch roof. Complex intersections need a measured roof plan and separate allowances for flashing, ridge, valley and starter products.
This is a geometric material estimate for a simple uniform-pitch shed or gable roof. It excludes detailed hips, valleys, dormers, flashing, ridge, starter courses, ventilation and structural design. Roof work is hazardous. Use measured plans and have a qualified roofer confirm quantities, installation rules and safe access.