Roof Pitch Calculator
Convert measured rise and run, an angle, or an x:12 pitch into equivalent roof-slope measurements.
Geometry Tool 3 of 6 · Output: Pitch · angle · slope % · F
2Calculate & check
Enter measurements to see the result and its calculation schedule.
3Limits
This is a conversion tool, not a roofing-material suitability check. A calculated slope does not establish drainage performance, minimum material slope or code compliance. Angles must be at least 0° and less than 90°.
How to use this calculator
- Choose the measurement you have: rise and run, an angle in degrees, or an x:12 pitch.
- Enter the measurement. Rise and run must describe the same right triangle.
- Calculate to compare pitch, degrees, percent slope and the area multiplier.
Formula & method
H is vertical rise and R is horizontal run. The angle θ is measured above horizontal. The area multiplier converts a horizontal projected area to a uniformly sloping surface area.
A worked example
Example inputs, not recommendations
A 6 in rise over a 12 in horizontal run gives a 6:12 pitch, approximately 26.5651°, a 50% slope and an area multiplier of 1.118034.
Assumptions & limitations
Assumes
- Rise and run use the same length units.
- The surface has one constant slope. Zero rise is accepted mathematically.
Does not cover
This is a conversion tool, not a roofing-material suitability check. A calculated slope does not establish drainage performance, minimum material slope or code compliance. Angles must be at least 0° and less than 90°.
Geometric planning estimate. This does not size structural members or verify loads, connections, or code compliance. Verify structural and code requirements against local code or with a qualified professional.
Displayed values are rounded; subsequent calculations retain full precision. Numerical limits and accepted formats are documented in Calculation methods.
Common questions
Does 50% slope mean 50 degrees?
No. Percent slope is rise divided by horizontal run, multiplied by 100. A 50% slope is approximately 26.565°, while a 45° angle is a 100% slope.
What does 6:12 mean?
The surface rises 6 units for every 12 horizontal units. The ratio works with inches, centimetres or any consistent length unit.
What is the area multiplier for?
Multiply a horizontal projection by this factor to find the corresponding sloping area. Use a separate multiplier for each different pitch.