How to use this roofing calculator
Calculate roof area, pitch factor, roofing squares, shingle bundles, underlayment, drip edge, tear-off, labor, and cost.
Formula
Sloped roof area = adjusted footprint × √(12² + rise²) ÷ 12. Roofing squares = area ÷ 100. Add waste, then round bundles and rolls up.Worked example
Example: A 40 × 28 ft building with 1 ft overhang and a 6:12 pitch has a pitch factor of about 1.118. Apply that factor to the adjusted footprint before adding waste.
Accuracy and limitations
This model assumes a simple gable roof. Hips, valleys, dormers, intersecting roofs, starter strips, ridge caps, flashing, ventilation, and access conditions need separate takeoffs.