Category

Roofing calculators

Roof geometry and material take-offs in one place: convert a building footprint and pitch into roof area, roofing squares and shingle bundles, or work backwards from run and rise to find pitch, rafter length and angle. Pitch in either x:12 or degrees, results in imperial squares and metric square metres.

All Roofing calculators

Geometry

Roof Pitch Calculator

Rise, rafter length and angle from run and pitch — or run and rise.
Material

Roofing Calculator

Roof area, squares and shingle bundles from footprint and pitch.

Footprint, pitch and the pitch factor

Roof area is not the same as building footprint. A 40 × 24 ft house with a flat roof has 960 ft² of roofing; the same house with a 6:12 pitch has 1,073 ft² — about 12 % more. The multiplier is the pitch factor: √(1 + (rise/run)²), or equivalently 1 / cos(angle). Always apply it before counting squares or bundles.

Squares, bundles and waste

In the U.S., roofing is sold in squares — 100 ft² of roof surface. Three-tab and architectural shingles typically come three bundles to a square, so a 12-square roof needs 36 bundles. Add a 10 % waste factor for cut-offs around hips, valleys, vents and chimneys, then round up to whole bundles. Steeper roofs (above 6:12) tend to waste more; complex roofs with many penetrations can hit 15 %.

Pitch in x:12 or degrees

U.S. carpentry uses x:12 — “X inches of rise per 12 inches of run”. Metric uses degrees. The conversions: angle = atan(x/12) × 180/π and x = tan(angle) × 12. A 6:12 is 26.6°; a 30° roof is about 6.93:12. Our roofing calculators accept both and convert automatically.