CalcRoof Pitch to Slope Converter
Last updated: 2026-08-24
How to Use This Roof Pitch to Slope Converter
This calculator transforms standard roof pitch notation (rise over run) into three essential values: slope angle in degrees, rise per foot of horizontal run, and the basic rafter length per foot of run. To use it, simply input your roof's rise in inches (the vertical measurement) and the run in inches (the horizontal measurement, typically 12 inches for standard pitch notation). The calculator instantly provides the corresponding slope angle and construction measurements needed for framing and material estimation.
Formula and Methodology
The conversion uses basic trigonometry. The slope angle equals the arctangent of the rise divided by the run, converted to degrees by multiplying by 180/π. Rise per foot is calculated by taking the rise-to-run ratio multiplied by 12. Rafter length derives from the Pythagorean theorem: the square root of rise squared plus run squared. This gives the true geometric length of the rafter for each foot of horizontal run, which is critical for accurate material cutting and roof framing.
Practical Examples
Example 1: Standard 6/12 Pitch
Rise = 6 inches, Run = 12 inches. Slope angle = arctan(6/12) × (180/π) = 26.57°. Rise per foot = (6/12) × 12 = 6 inches. Rafter length = √(6² + 12²) = 13.42 inches per foot of run.
Example 2: Low Slope 2/12 Pitch
Rise = 2 inches, Run = 12 inches. Slope angle = arctan(2/12) × (180/π) = 9.46°. Rise per foot = 2 inches. Rafter length = √(2² + 12²) = 12.17 inches per foot of run. This is common for commercial or flat-style residential roofs.
Example 3: Steep 12/12 Pitch
Rise = 12 inches, Run = 12 inches. Slope angle = arctan(12/12) × (180/π) = 45°. Rise per foot = 12 inches. Rafter length = √(12² + 12²) = 16.97 inches per foot of run. This dramatic pitch is often used for cathedral ceilings and A-frame structures.
Example 4: Non-Standard Run
If you have a run of 10 inches with a rise of 5 inches (like some shed roofs), input rise=5, run=10. Slope angle = 26.57°, rise per foot = 6 inches (scaled), and rafter length = 11.18 inches per foot of run. This shows how the tool adapts to any rise/run combination.
Tips and Best Practices
Always measure roof pitch from the actual roof deck, not from ceiling joists. For accurate results, ensure the run measurement is precisely horizontal and the rise is perfectly vertical. When buying materials, multiply the rafter length per foot by the total horizontal span (in feet) to estimate total rafter length, then add for overhangs and ridge boards. Double-check your pitch calculations before cutting rafters — a small degree error can compound into significant misalignment. For complex roofs with multiple pitches, calculate each section separately. Use the degrees output for compatibility with solar panel mounting systems, skylight installation, and building code compliance where maximum slope requirements apply.
FAQ
What is a 6/12 roof pitch in degrees?
A 6/12 roof pitch equals approximately 26.57 degrees. This is calculated by taking the arctangent of 6/12 (rise divided by run) and converting radians to degrees.
How do I convert roof pitch to slope percentage?
Slope percentage is (rise/run) × 100. For a 6/12 pitch, that's (6/12)×100 = 50%. Our calculator gives you the angle in degrees first.
What roof pitches are common for residential homes?
Common residential roof pitches range from 4/12 (18.43°) to 9/12 (36.87°). Low-slope roofs are 2/12 (9.46°) or less, while steep roofs go up to 12/12 (45°).
Does rafter length include overhang?
No, the rafter length shown is the basic length from ridge to birdsmouth for the given rise and run. You'll need to add overhang length separately for your full rafter cuts.