Calculate total roof surface area for gable, hip, and shed roofs. Estimate roofing material quantities including waste factor.
Enter the building length and width in feet, the pitch as rise per 12, and the rafter spacing in inches on-center. The footprint (length × width) is multiplied by the pitch factor √(1 + (rise/12)²) to convert flat plan area into actual sloped roof surface — 1.118 at 6/12, 1.414 at 12/12.
Results include the area in square feet and in roofing squares (1 square = 100 sq ft), three-tab shingle bundles at 3 bundles per square rounded up to whole bundles, and 4 × 8 plywood sheathing at 32 sq ft per sheet, also rounded up.
A 40 × 30 ft building at 6/12 works out to about 1,342 sq ft of surface, 13.42 squares, 41 bundles, and 42 sheets. Rafter count uses floor(length in inches ÷ spacing) + 1 per side, doubled — 62 rafters at 16 inch centers. No separate waste percentage is added, so order extra for hips, valleys, and cuts.
A unit of 100 square feet of roof surface. Suppliers price shingles by the square, and standard three-tab shingles pack 3 bundles to the square — exactly the conversion this calculator uses before rounding up to whole bundles.
It converts the flat footprint into true sloped area: √(1 + (rise/12)²). A 4/12 roof has about 5.4% more surface than its footprint (factor 1.054), a 6/12 has 11.8% more, and a 12/12 has 41.4% more — steep roofs need substantially more material.
Sheathing count is roof area ÷ 32 — the coverage of one 4 × 8 sheet — rounded up. A 1,342 sq ft roof needs 42 sheets; the rounding only covers fractional sheets, not cutting losses around edges and openings.
No. Quantities are rounded up to the next whole bundle and sheet, but no percentage allowance is applied for hips, valleys, starter courses, or damaged material. Treat the numbers as the geometric minimum and order extra for complex roofs.