What does roof pitch mean?
In common U.S. construction notation, roof pitch is usually expressed as inches of vertical rise for every 12 inches of horizontal run. A 6:12 roof rises 6 inches for every 12 inches of run.
Common roof pitch examples
- 3:12 — 3 inches of rise for each 12 inches of horizontal run
- 4:12 — 4 inches of rise for each 12 inches of run
- 6:12 — 6 inches of rise for each 12 inches of run
- 8:12 — 8 inches of rise for each 12 inches of run
- 12:12 — equal rise and run
Convert roof pitch to slope percentage
Slope percentage compares vertical rise with horizontal run and multiplies the ratio by 100.
Convert pitch to roof angle
The roof angle is the arctangent of rise divided by run. For example, a 6:12 pitch corresponds to an angle of approximately 26.6 degrees.
What is roof slope factor?
The slope factor converts horizontal projected area into sloped roof surface area. Steeper roofs have larger slope factors because the roof surface travels farther than the horizontal footprint beneath it.
Why roof pitch matters
- It affects roof surface area.
- It changes roofing-material quantities.
- It influences drainage and roof geometry.
- It affects access and installation difficulty.
- Some roofing products have minimum-slope requirements.
Measuring an existing roof can involve fall hazards. Use measurements available from plans, attic spaces or safe ground-based methods where possible.