Roof Pitch Calculator
Convert roof rise and run into pitch angle, slope factor and grade.
Multiply the roof footprint by the slope factor for sloped area. A design guide — follow local codes and a structural professional for builds.
Rise over run, four ways
Roof slope is the ratio of vertical rise to horizontal run. Builders quote it as an x-in-12 pitch, designers prefer degrees, and material estimates use the slope factor — all describe the same incline.
angle = arctan(rise ÷ run) · slope factor = √(rise² + run²) ÷ run
The slope factor is the practical payoff: the true sloped surface is always larger than the flat footprint beneath it, and this multiplier tells you by how much when ordering roofing materials.
A 6-in-12 roof rises 6 for every 12 of run — a pitch of about 26.57°, a 50% grade, and a slope factor of roughly 1.118, so the sloped roof area is about 12% more than its footprint.
Choosing and using pitch
Steeper roofs shed rain and snow readily and add attic space, but use more material and are harder to work on. Lower pitches are economical but demand careful detailing to stay watertight. The slope factor keeps material orders honest either way.
On-site notes
- Order by sloped area. Footprint × slope factor, not the flat plan.
- Mind low pitches. They need extra waterproofing care.
- Match the units. Rise and run must share a unit for a clean ratio.