Roof Pitch Calculator — Free & Easy
Calculate a roof’s pitch, angle in degrees, slope percentage and sloped rafter line from measured rise and horizontal run. Switch between feet, inches, centimeters and meters.
Loading the interactive calculator. Enable JavaScript to enter your values, or use the formulas and worked example below.
How to use the Roof Pitch Calculator
Calculate a roof’s pitch, angle in degrees, slope percentage and sloped rafter line from measured rise and horizontal run. Switch between feet, inches, centimeters and meters.
- Step 1. Measure the horizontal run—not the sloped roof edge.
- Step 2. Measure the vertical rise over the same run.
- Step 3. Select the shared measurement unit, enter both measurements and read the pitch, angle and slope percentage.
- Step 4. For installation work, account separately for overhangs, ridge dimensions and local structural requirements.
Important: This is a mathematical geometry estimator, not roof engineering advice.
Roof Pitch Calculator formula explained
Roof pitch per 12 = (vertical rise ÷ horizontal run) × 12. Angle (degrees) = arctan(rise ÷ run) × 180/π. Slope percentage = rise ÷ run × 100.
All calculator outputs depend on the measurements, units and assumptions you enter. Intermediate calculations use unrounded numeric values; formatted results may be rounded for easier reading. For any consequential purchasing or construction decision, verify supplier specifications and regulations.
Worked example with real numbers
A rise of 6 inches across a horizontal run of 12 inches is a 6:12 pitch, 50% slope and about 26.57°. The straight slope length across that run is √(6² + 12²), or about 13.42 inches.
The example illustrates the formula independently of the interactive fields. You can change the values above to match your own project and compare results.
Frequently asked questions
How do I convert 6:12 pitch to degrees?
Calculate arctan(6 ÷ 12) = approximately 26.57°. This is a geometric angle, not a building-code approval.
Is roof pitch the same as slope percentage?
They describe the same relationship in different units. A 6:12 pitch is 50% slope.
Can I use centimeters rather than inches?
Yes. Pitch is a ratio, so using the same unit for rise and run produces the same angle and pitch.
Does the sloped length include the roof overhang?
No. The calculator uses only the rise and run entered; extensions and construction cuts must be added separately.