Roofing calculator
Roof Pitch Calculator
Convert measured vertical rise and horizontal run to pitch, angle, slope factor, and sloped length.
Planning estimate, not a contractor quote. Review the assumptions and replace presets with local prices when available.
Method
How this calculator works
Roof pitch expresses how much the roof rises over a fixed horizontal distance. Enter rise and run measured in the same system; the calculator also reports the factor used to convert horizontal area to sloped area. This geometric conversion does not determine whether a particular roofing product can be installed at that pitch.
Pitch rise per 12 = rise ÷ run × 12. Angle = arctan(rise ÷ run). Slope factor = √(1 + (rise ÷ run)²). Sloped length = √(rise² + run²).
Worked example
A realistic starting point
A 6-inch rise over a 12-inch horizontal run gives a 6:12 pitch, a 26.565° angle, a 1.1180 slope factor, and a 13.416-inch sloped length for that measured segment.
What changes the answer
Factors worth checking
Horizontal run
Run is the horizontal leg of the right triangle. It is not the length measured along the sloping rafter.
Unit consistency
Metric mode converts both legs together. A ratio remains unchanged when the same unit conversion is applied to rise and run.
From pitch to roof area
Multiply horizontal projected roof area by the slope factor only for areas with that pitch. Different roof planes need their own measurements.
Common questions
Roof Pitch FAQ
What is a 4:12 pitch?
It rises 4 units vertically for each 12 horizontal units, a slope of one third.
Is angle the same as pitch?
They describe the same slope differently: angle uses degrees and pitch uses a rise-to-run ratio.
Can I enter centimeters?
Yes. Metric mode accepts centimeters for both measured legs. The pitch ratio remains dimensionless.
Evidence
Sources & review
- NIST — SI units: volumeUnit relationships; supplier product coverage and prices remain separate inputs.
Published by Calcstead. Report a correction.
Method and source links reviewed September 6, 2026. Price presets are editable planning inputs and should be replaced with current local information.