Roof Pitch Calculator
Calculate roof pitch ratio, approximate slope angle in degrees, and rafter length from rise and run measurements.
Results
What is it?
The Roof Pitch Calculator converts a rise-over-run measurement into the standard X:12 pitch notation, estimates the slope angle in degrees, and calculates the rafter length (common rafter) from the total roof span. The pitch ratio tells you how many inches the roof rises for every 12 inches it runs horizontally.
How to use
1. Enter the rise in inches (how much the roof rises vertically). 2. Enter the run — typically 12 for standard pitch notation. 3. Enter the total roof width (horizontal span) in feet. 4. Read the pitch ratio, approximate angle, and rafter length.
Example scenario
A 6:12 pitch roof over a 24 ft wide house: pitch = 6:12, angle ≈ 26.6°, rafter length = 24/2 × √(1 + (6/12)²) = 12 × 1.118 ≈ 13.4 ft per rafter.
Pro tip
A 4:12 pitch is the minimum for most asphalt shingles. Pitches below 2:12 require special low-slope roofing materials. The roof multiplier × total roof area gives you the actual surface area of the roof — critical for ordering shingles.