Roof pitch calculator
Convert between roof pitch in degrees, ratio and percentage, and get rafter length.
How it works
Converts roof pitch between the three ways it gets expressed \u2014 degrees, a rise-over-run ratio, and a percentage \u2014 and calculates the rafter length for a given span.
The ratio conventions differ by country and are a genuine source of confusion. In the United States pitch is written as rise in inches per 12 inches of run, so 6:12 means six inches of rise per foot, or 26.6 degrees. In much of Europe it is stated in degrees directly, and in road and drainage work as a percentage, where 100% is 45 degrees rather than vertical.
Rafter length is the hypotenuse: the square root of rise squared plus run squared. It is always longer than the run, which is why roof area exceeds the footprint of the building \u2014 a 30-degree roof has about 15% more surface than the floor beneath it, and that matters when ordering covering.
This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.
Common questions
- What does a 6:12 roof pitch mean?
- Six units of rise for every twelve of run \u2014 26.6 degrees. It is the common American way of writing pitch.
- How do you convert roof pitch to degrees?
- Take the arctangent of rise divided by run. A 6:12 pitch is arctan(6/12) = 26.57 degrees.
- Is roof area the same as floor area?
- No, it is always larger. A 30-degree pitch adds about 15% and a 45-degree pitch about 41%.
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Sources
- Calculated on this page — At One Place