Roof pitch calculator
Convert roof pitch between percentage, degrees and x:12 ratio, calculate the ridge height from the span and the true roof area with the pitch factor.
How to useRoof pitch in %, degrees and height
Available in: 
Roof pitch calculator: what it is for
Enter the pitch as a percentage, in degrees or by rise and run. The tool converts between percentage, degrees and the x:12 ratio, calculates the area correction factor, the ridge height and the rafter length from the building span, and the true roof area for a shed or gable roof, with a profile drawing.
The calculations run in your browser and are estimates; confirm quantities with your supplier or a professional before buying.
How to use
- Choose how you'll enter the pitch.
- Type the span and the roof length.
- See the results and the drawing.
When to use it
- Designing a new roof.
- Checking whether the pitch suits the chosen roofing.
- Calculating the true area to buy roofing and underlayment.
Frequently asked questions
How is pitch measured as a percentage?
It's the height the roof rises divided by the horizontal run, times 100. A roof that rises 35 cm for every 1 m has a 35% pitch, which is about 19.3 degrees. 100% equals 45 degrees, not a vertical roof.
How do I calculate the ridge height?
Multiply the pitch by half the span on a gable roof. With an 8 m span and 30%, each side covers 4 m horizontally and the ridge sits 4 × 0.30 = 1.20 m above the support.
What is the minimum pitch for each roofing type?
It varies by product and manufacturer. As a common reference, clay tiles usually require 30% to 35% or more, concrete tiles around 30%, fiber cement from about 10% to 15% and metal roofing from about 5% to 10%. Always follow the manufacturer's specifications.
Is it really free?
Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 tools are free and run right in your browser.