Shingle squares, underlayment rolls, ridge caps & nails
Enter your building footprint (length × width at the eaves), select the roof pitch, and the calculator applies the correct roof pitch multiplier to convert the flat footprint into actual sloped roof area. From that it derives squares of shingles, bundles, underlayment rolls, ridge cap bundles, and nail quantities — all adjusted for a waste factor.
A 40 ft × 24 ft gable house with a 6/12 pitch: footprint = 960 sq ft, sloped area = 960 × 1.118 = 1,073 sq ft ≈ 10.7 squares. Ridge length = 40 ft. With 10% waste: order 11.8 squares ≈ 36 bundles, 12 rolls of #30 felt, and 2 bundles of ridge cap. At $35/bundle that's about $1,260 in shingles.
How many bundles of shingles make a square? Three bundles cover one square (100 sq ft) for most standard-weight 3-tab and architectural shingles. Some premium heavyweight shingles are 4–5 bundles per square — check the bundle label.
What is a roof pitch multiplier? It is the ratio of sloped roof length to horizontal run — the hypotenuse of the pitch triangle. For 6/12: √(6²+12²)/12 = 1.118.
What waste factor should I use? 10% for simple gable roofs, 12–15% for hip roofs and roofs with many valleys, dormers, or chimneys.
How is a hip roof different? A hip roof has four sloped planes and hip ridges, so ridge/hip cap material runs along all four hips plus the main ridge — typically 1.5× the cap length of a comparable gable roof.