Roof Pitch and Rafter Calculator 🏠

How to Use the Roof Pitch Calculator

Select your measurement system (imperial or metric), enter the total building span (width) and the roof rise (vertical height from wall top to ridge). The calculator automatically computes the roof pitch, angle, and rafter length needed for your roofing project.

Understanding Roof Pitch

Roof pitch is the steepness of a roof expressed as a ratio of vertical rise to horizontal run. In the US, it's commonly expressed as "x:12" (how many inches the roof rises for every 12 inches of horizontal distance). For example, a 6:12 pitch means the roof rises 6 inches for every 12 inches of run.

Common Roof Pitch Applications

• Low slope (2:12 to 4:12): Modern homes, prairie-style architecture, easier to work on but requires proper waterproofing
• Medium slope (4:12 to 9:12): Most common for residential homes, good balance of drainage and walkability
• Steep slope (9:12 and up): Traditional designs, excellent drainage, more material needed, challenging to work on
• Flat (less than 2:12): Commercial buildings, requires special roofing materials and drainage systems

Typical Roof Pitch Reference