DIY Cost Tools
Roof Pitch Calculator
HOME & OUTDOOR PLANNING
Convert roof rise and horizontal run into pitch, angle, percent slope, and a length multiplier.
Use the units shown. All fields are required; absolute values cannot exceed one trillion. Measure horizontal run, not the sloped rafter length. This tool does not verify load capacity, roofing-product suitability, drainage, or building-code compliance. Measure safely from the ground or use a professional.
How to use this calculator
Replace the example inputs with your own measured values, using the units beside each field. Select Calculate, then compare results under different practical assumptions. Keep extra precision in measurements until the final answer.
Formula and explanation
Pitch = 12 × rise/run; angle = arctan(rise/run); slope % = 100 × rise/run; multiplier = √(rise²+run²)/run
A 6-in-12 pitch rises six inches for every twelve horizontal inches. The multiplier converts horizontal distance to the corresponding sloped distance.
Worked example
With Vertical rise (inches) = 6, Horizontal run (inches) = 12, the results are Rise per 12 inches of run: 6; Roof angle (degrees): 26.565051; Slope (%): 50; Slope-length multiplier: 1.118034.
Important limitations
Measure horizontal run, not the sloped rafter length. This tool does not verify load capacity, roofing-product suitability, drainage, or building-code compliance. Measure safely from the ground or use a professional.
These are planning estimates. Confirm actual measurements, product instructions, site conditions, and any applicable project requirements before purchase or installation.
Frequently asked questions
Does 6-in-12 mean 6 degrees?
No. It is a rise-to-run ratio; its angle is about 26.57 degrees.
Can the roof be flat?
Zero rise is supported mathematically, but a zero result does not establish adequate drainage.
Can I mix measurement units?
No. Convert values to the units shown beside the fields first. The result labels identify the output units.
What happens when inputs are invalid?
Blank, negative where disallowed, nonfinite, or out-of-range values clear the old results and show an instruction.
Review notes
Reviewed October 1, 2026. Default examples were checked independently against the displayed equations and conversion factors. Page-script tests covered blank, negative, nonfinite, and excessive inputs. Calculations run locally in your browser.