Roof Pitch Calculator
Roof pitch is how steep the roof is — the rise over a run. Enter the rise and run and this gives the pitch in the usual x-in-12 form, plus the angle, the slope multiplier, and the percent grade.
Pitch
6in 12
- Angle
- 26.6 °
- Slope multiplier
- 1.118 ×
- Percent grade
- 50 %
How it’s calculated
Pitch (in 12) = rise ÷ run × 12. Angle = arctan(rise ÷ run), in degrees. Slope multiplier = √(rise² + run²) ÷ run — how much longer the sloped surface is than its run (multiply a footprint by it to get roof area). Percent grade = rise ÷ run × 100.
Worked example
A roof rising 6 inches over 12 inches of run: 6 ÷ 12 × 12 = a 6-in-12 pitch; arctan(0.5) ≈ 26.6°; √(6² + 12²) ÷ 12 ≈ 1.118 ×; 50% grade.
FAQs
- What does “6 in 12” mean?
- The roof rises 6 inches for every 12 inches of horizontal run. Pitch is quoted over a 12-inch run by convention, so a 6/12 is moderately sloped and a 12/12 is a steep 45°.
- How do I measure rise and run?
- Hold a level out horizontally from the roof, mark 12 inches along it (the run), and measure straight down from that point to the roof surface (the rise). A pitch finder or a phone app works too.
- What's the slope multiplier for?
- It converts a flat footprint into actual roof area: footprint × multiplier = roof surface. A 6/12 roof's 1.118 means the surface is about 12% bigger than the ground it covers — see the roof area calculator.
Sources
- Pitch = rise ÷ run × 12; angle = arctan(rise ÷ run); slope multiplier = √(rise² + run²) ÷ run; grade = rise ÷ run × 100. Trigonometry.