Roof pitch is traditionally expressed as rise over a 12-inch run (e.g. 4:12, 6:12, 8:12) in imperial construction. Civil engineering and drainage planning, however, measure slope as a percentage (e.g. 50%). Free Online Protractor automatically translates between incline angle, pitch ratio, and slope grade % instantly.
1. The Mathematics of Pitch Ratio (X : 12)
Angle (Degrees) = arctan(Rise / 12) * (180 / π). For example, a 6:12 pitch has a rise of 6 inches over 12 inches of horizontal run, resulting in arctan(0.5) = 26.57°.
2. Converting Pitch to Slope Grade Percentage
Slope grade percentage equals (Rise / Run) * 100%. A 12:12 pitch (45.0°) represents a 100% slope grade, while a 6:12 pitch equals a 50.0% grade.
3. Using Roof Pitch Mode on Site Photos
Switch the protractor mode to "Roof Pitch" in the mode selector. Align the baseline along the roof truss horizontal line and the slope ray along the rafter edge for automatic rise-over-12 output.
Key Technical Takeaways
- A 6:12 pitch corresponds to 26.57° incline and 50% slope grade.
- Roof Pitch Mode formats outputs directly for building code specifications.
- Instant unit conversion saves time during framing estimation and inspection.