Roof pitch calculator
Roof pitch, angle and percent slope from rise and run, plus roof area in squares from the footprint.
How it's calculated
Measure the rise over a known run (12 inches is standard) to get the pitch, angle and percent slope. Add the footprint area to estimate the sloped roof area in roofing squares.
pitch = rise ÷ run × 12 (written x:12)
angle = arctan(rise ÷ run)
slope % = rise ÷ run × 100
pitch multiplier = √(1 + (rise ÷ run)²)
roof area = footprint × multiplier × (1 + waste %)
squares = roof area ÷ 100
Worked example
A 6 in rise over 12 in is a 6:12 pitch: 26.57° or 50% slope, with a multiplier of 1.118. A 12:12 roof over a 1,500 sq ft footprint has 1,500 × 1.414 = 2,121 sq ft of roof; with 10% waste that is 2,333 sq ft, or 23.3 squares.
The multiplier method assumes all roof planes share one pitch. Dormers, valleys and mixed pitches need a plane-by-plane takeoff.
Sources
- Slope expressed as inches of rise per 12 inches of run, and 1 roofing square = 100 sq ft: NRCA Steep-Slope Roofing Materials Guide.
- Angle and multiplier follow from right-triangle trigonometry.
Working on a roof is dangerous; use fall protection or hire a professional.