Roof Pitch Calculator - Pitch, Angle, Slope, Rafter Length & Roof Area
Roof Pitch Calculator
Convert between roof pitch, angle and slope, and size your rafters
Every Way to State a Pitch
Enter rise per 12, degrees, percent slope or rise and run and see all the others at once.
Rafter Length
Give the building width and overhang to get the rafter length along the slope and the ridge height.
Roof Area
Multiply the plan area by the area factor to get the real roof surface for roofing materials.
Full Privacy
Everything is calculated in your browser.
Reading a Roof Pitch
In North America a pitch such as 6:12 means the roof rises 6 inches for every 12 inches of horizontal run. That is a slope of 50%, an angle of 26.57°, and a surface 1.118 times longer than its horizontal projection. A 12:12 roof is 45° and 100%, and a 4:12 roof, about 18.4°, is around the lowest pitch for many shingles.
The rafter length is measured along the slope from the ridge to the tail of the overhang: half the span plus the overhang, times the area factor. It does not include the cut for the ridge board or birdsmouth, so allow extra when ordering lumber. Minimum pitches, snow load and wind rules vary by roofing material and location, so check local building codes.
Key Takeaways
- Exact trigonometry: Uses tan, cos and the Pythagorean area factor, not rounded lookup tables.
- Both unit systems: Lengths and areas convert between metric and imperial.
- Estimate: Confirm dimensions with your plans and local codes.