FIELD GEOMETRY / FREE CALCULATOR
Roof pitch calculator: rise, run and angle
Enter the vertical rise and horizontal run of one roof slope. Get its pitch in rise per 12, angle, percentage slope and straight rafter line length. All calculations run in your browser.
YOUR DIMENSIONS / YOUR BROWSER
Calculate the geometry
Worked example: 6 inches of rise over 12 inches of run
- Divide rise by run: 6 ÷ 12 = 0.5.
- Multiply by 12 for the pitch ratio: 6:12.
- Take arctan(0.5) for the angle: 26.565°.
- Multiply the ratio by 100: 50% slope.
- Use √(6² + 12²) for the sloping line: 13.416 inches.
Run is different from the full roof span
Run is the horizontal distance under the slope you are calculating. For a symmetric gable roof it is usually half the full span, before allowances. Using the full span for one slope would understate its angle. Here “pitch” means rise per 12 units of run, the common calculator convention.
What the rafter result includes
The result is the hypotenuse of a right triangle. It does not account for an overhang, ridge-board deduction, birdsmouth, material thickness or cutting allowance. Confirm those separately before preparing a cut list.
Does a pitch result mean a roof design is suitable?
No. This is a geometry calculation. It does not select roofing materials, check loads or establish compliance. Use the dimensions, product requirements and design documents for your project.
TAKE IT TO THE JOB
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Original calculator by Eutopix Labs · Published 15 September 2026.