Roof Pitch Calculator
Roof pitch determines shingle selection, drainage performance, and walk-ability. This calculator converts rise and run measurements into the standard pitch ratio (X:12), angle in degrees, slope percentage, and rafter length factor used in roof framing.
Roof pitch is expressed as a ratio of rise to run, where run is standardized to 12 inches. A "6:12 pitch" means the roof rises 6 inches for every 12 inches of horizontal distance. The three common ways to express the same slope are: pitch ratio (6:12), angle (26.57°), and slope percentage (50%).
The rafter length factor tells you the diagonal distance (along the rafter) for each 12 inches of horizontal run. For a 6:12 pitch, the factor is 13.416 inches, meaning a rafter spans 13.416 inches diagonally for every 12 inches horizontally. Multiply this by the total run in feet to get the rafter length.
Pitch affects material selection: flat to low-slope roofs (below 2:12) require membrane or built-up roofing. Standard asphalt shingles require a minimum 2:12 pitch (4:12 recommended). Slate and tile need 4:12 minimum. Metal roofing can work from 1:12 up. Steeper pitches shed water and snow faster but use more materials and are harder to walk on.