Interpretation
A 6:12 roof rises 6 units for every 12 units of horizontal run. Pitch, slope percent and angle describe the same geometry in different formats.
Example
If rise is 6 and run is 12, pitch is 6:12. The angle is arctan(6 / 12), or about 26.6 degrees, and the slope is 50%.
Common mistakes
Run is horizontal distance, not the sloped rafter length. Using rafter length as run will understate the true pitch.
Limitations
Roof work can involve fall hazards, structure, drainage and local codes. This page only calculates geometry and does not approve a roof design.
Last reviewed: 2026-05-17