Formula and input notes
Roof area = plan length × plan width × slope factor × (1 + waste ÷ 100); roofing squares = area ÷ 100
| Input | Practical note |
|---|---|
| Slope factor | The slope factor converts horizontal plan area to sloped surface area. Derive it from the actual pitch rather than choosing it from appearance. |
Worked roof shingle example
Roof Shingle Calculator example: 50.8 ft × 25.2 ft × 1.12 × 1.1 = 1,577.16 ft², or 15.77 roofing squares.
Read squares and sloped area
Round to whole bundles after applying waste and keep starter and ridge-cap products separate unless the manufacturer permits field fabrication.
Geometry and accessories outside the total
Valleys, hips, ridges, starter strips, cut tabs, laminated-shingle exposure, bundles per square, and complex geometry affect the order.
Questions specific to this calculation
How do roofing squares relate to shingle bundles?
Convert each roof plane from plan area to sloped area, then use shingle coverage per bundle or square from the selected product.