Roof pitch & area calculator
Turn your home's footprint and roof pitch into the actual sloped roof area — the number the shingle calculator needs. The pitch multiplier is pure right-triangle geometry, so a steeper roof has more surface than the floor beneath it.
1,342 sq ft
Roof surface area
- Roofing squares
- 13.4 squares
- Pitch multiplier
- 1.118 ×
- Footprint area
- 1,200 sq ft
What this assumes
- Pitch multiplier = √(6² + 12²) ÷ 12 = 1.118.
- Roof area = 40 ft × 30 ft footprint × 1.118 = 1342 sq ft.
- One roofing “square” = 100 sq ft.
Coverage rates & sources
Every number this calculator uses is a published engineering constant — not an estimate we made up. Here is exactly what it assumes and where each value comes from.
- Pitch multiplier: √(rise² + 12²) ÷ 12Source: Roof slope geometry — Pythagorean theorem on the rise/run right triangle
- Roofing square: 100 ft²Source: Roofing industry standard unit of area
Before you buy
- Assumes a simple gable or hip footprint where the whole roof shares one pitch. Dormers, valleys, multiple pitches, and complex shapes need a plane-by-plane takeoff.
- Measure the footprint to the edge of the overhangs (eaves and rakes), not the exterior walls, or you'll undercount.
- This is roof area only — feed it into the shingle calculator for bundles, and add that calculator's waste factor there.
This is a planning estimate, not a substitute for a pro's on-site measurement. For load-bearing, structural, or code-regulated work, confirm quantities with a licensed contractor.
Frequently asked
What is a roof pitch multiplier?
It's the ratio of sloped length to horizontal run from the right triangle a roof forms: √(rise² + run²) ÷ run. With run fixed at 12, a 4/12 roof is 1.054×, an 8/12 is 1.202×, and a 12/12 (45°) is 1.414×.