How do I calculate roof pitch?
Convert rise and run into pitch notation, angle, and a slope factor for planning.
Short answer
Measure the vertical rise and horizontal run in matching units, divide rise by run, and express the result as rise over a 12-unit run.
For homeowners checking a roof measurement before an early surface-area estimate.
How to do it
Measure rise and run
Use the same unit for the vertical rise and horizontal run.
Enter both values
Use the Roof Pitch Calculator and check that the run is greater than zero.
Review the outputs
Read the :12 pitch, equivalent angle, and slope factor together.
Use the value carefully
Pass the slope factor to a simple planning estimate only when the roof is represented by that one slope.
Formula
Pitch12 equals rise divided by run multiplied by 12. Angle is arctangent of rise divided by run. Slope factor is the square root of 1 plus the squared ratio.
Illustrative example
A 6 inch rise over a 12 inch run is a 6:12 pitch, about 26.565 degrees, with a slope factor of approximately 1.118034.
Common mistakes
- Mixing inches and feet without converting
- Treating pitch as the full roof area
- Assuming every roof plane has the same slope
Before you buy
Use pitch as one input among the roof measurements. Have unusual, inaccessible, or multi-plane roofs checked by a qualified professional.
What this guide does not cover
Pitch describes one slope only. It cannot model the whole roof, dormers, valleys, hips, or safe access conditions.
Use the calculator
Roof Pitch Calculator is the primary tool for this guide. You can also browse the other roofing calculators.