Roofing Calculator
Roof area, squares, and shingle bundles from your footprint and roof pitch.
Rise per 12″ of run. 0 = flat.
- Slope factor 1.118 at 6:12 — roof area is the 1200 sq ft footprint × that factor.
- A "square" is 100 sq ft. Order ~10% extra for waste, starter, and hip/ridge caps (typical — check your product).
- Bundles assume ~3 per square (typical 3-tab / architectural). Complex roofs — dormers, valleys, overhangs beyond the footprint — add area; measure or add margin.
How the roofing estimate works
The roof covers a footprint (length × width), but a slope adds surface. The
slope factor — √(rise² + 12²) ÷ 12 — scales the
footprint up the slope, so roof area = footprint × slope factor.
That reuses the same geometry as the
roof pitch converter.
Roof area ÷ 100 gives squares, the roofing unit; a waste allowance covers offcuts, starter, and caps. Bundles assume roughly 3 per square (typical) — check your product. This works for a symmetric gable or hip over a rectangle; dormers, valleys, and overhangs beyond the footprint add area, so measure or add margin on a cut-up roof.
Frequently asked questions
What is a roofing square?
A "square" is 100 square feet of roof surface — the unit shingles and roofing labor are quoted in. A 1,340 sq ft roof is about 13.4 squares.
How does roof pitch change the area?
A sloped roof has more surface than the footprint it covers. The slope factor is √(rise² + 12²) ÷ 12 — about 1.12 at 6:12 and 1.41 at 12:12 — so the roof area is the footprint times that factor. A flat (0:12) roof factor is 1.
How many shingle bundles do I need?
Most three-tab and architectural shingles run about 3 bundles per square. Multiply squares (including waste) by 3 and round up. Add extra for starter strips and hip/ridge caps, and check your specific product's coverage.