Roofing Calculator
Calculate roof area and roofing squares from dimensions and pitch factor.
Ordering the right amount of roofing material starts with accurately measuring the roof surface area. Because roofs are sloped, the true surface area is larger than the building footprint.
The pitch factor converts a flat (plan) measurement to the actual sloped area. A 4/12 pitch (the most common residential pitch) has a factor of 1.118, meaning the roof is about 12% larger than the footprint. Steeper pitches like 8/12 have a factor of 1.202.
Roofing materials are sold in "squares" — one square covers 100 square feet (9.29 m²). Asphalt shingles typically come three bundles per square. Always add 10–15% for waste from hips, valleys, and starter courses. Complex roof shapes with dormers and valleys waste more material than simple gables.