Roof pitch, expressed the standard US roofing way — as a rise per 12 units of horizontal run — plus the equivalent angle in degrees.
How it works
Dividing rise by run and multiplying by 12 gives the “x-in-12” pitch notation; the arctangent of rise over run gives the equivalent angle.
What this does not include
This does not include material or shingle-count estimates — for that, use this site’s roofing calculator instead. This tool converts rise/run to pitch and angle only.
How to use this calculator
- Enter the rise and run.
A worked example
A roof that rises 6 inches for every 12 inches of horizontal run is a 6-in-12 pitch, equivalent to a 26.57° angle.
A rise of 4 inches over the same 12-inch run gives a 4-in-12 pitch, a shallower 18.43° angle.
What the variables mean
| Variable | Meaning |
|---|---|
| Rise | Vertical height gained |
| Run | Horizontal distance the rise happens over (conventionally 12 inches in roofing) |
Edge cases worth knowing
Roof pitch is conventionally expressed per 12 inches of run — “6-in-12” is the standard way roofers describe slope, distinct from the angle-in-degrees a protractor would read.
A run of zero makes the pitch undefined — a perfectly vertical rise with no horizontal run isn’t a roof slope this formula can express.
Frequently asked questions
What does “6-in-12” mean?
The roof rises 6 inches vertically for every 12 inches of horizontal run — a common way roofers express slope without needing degrees.
Why is run conventionally set to 12?
It’s simply the standard US roofing convention for expressing pitch as a whole-number-friendly ratio, not a requirement of the underlying math.
What’s considered a steep roof pitch?
Pitches above about 9-in-12 (roughly 37 degrees) are generally considered steep, though what’s practical depends on the roofing material and local building codes.
