Roofing Calculator
Estimate a simple roof’s surface area from horizontal dimensions and pitch, or enter directly measured surface dimensions. Allow for overhang and purchasing waste.
Your result
How the calculation works
Footprint area = (length + 2 × overhang) × (width + 2 × overhang). Pitch factor = √[1 + (rise ÷ 12)²]. Surface area = footprint × pitch factor. Roofing squares = order area in ft² ÷ 100. Bundles or sheets = round up(order area ÷ effective coverage).
Worked example
A 10 m × 8 m footprint with no overhang and a 6:12 pitch has an 80 m² plan area. Pitch factor is 1.1180, giving 89.44 m² surface. Add 10% waste for 98.39 m², or about 10.59 roofing squares.
Assumptions and limitations
Footprint mode assumes one constant pitch across a simple roof. Surface mode uses length × width and ignores pitch and overhang. Coverage must account for actual overlaps. The result does not model hips, valleys, dormers, ridges or varying slopes.
Separate complicated roofs into measured surfaces, then confirm takeoffs with a roofer. Waste depends on roof geometry and material. Roofing squares are an area unit, not a number of shingles. Do not access a roof without appropriate professional safety arrangements.
Common questions
What is a roofing square?
One roofing square is 100 square feet of roof surface.
Method reviewed 2026-10-07. Calculation standards · Report an issue