Roof Pitch Calculator
Find roof pitch as a ratio, the angle in degrees, and the slope factor for area work, all from the rise and run.
Rise is the vertical height; run is the horizontal distance, usually measured over a standard 12 inches. Pitch is read as the rise in 12, so a rise of 6 over a run of 12 is a 6/12 pitch.
Enter the rise and run to find the pitch and angle.
How to use the roof pitch calculator
Enter the rise, the vertical height the roof climbs, and the run, the horizontal distance it covers. Run is normally measured over a standard 12 inches. The calculator returns the pitch as a ratio, the angle in degrees, and the slope factor for area work.
You can measure rise and run with a level and a tape on the roof or in the attic against a rafter. Keep both in the same unit; the ratio and the angle depend only on their proportion, not the unit you use.
What roof pitch means
Pitch describes how steep a roof is, written as the rise over a 12-unit run, such as 6/12. That reads as six inches of vertical rise for every twelve inches of horizontal run. A higher first number means a steeper roof.
The 12-unit run is the US convention, which is why pitches are almost always quoted as something over 12. The calculator normalizes whatever run you enter to that 12 base, so a measured 5 rise over a 10 run reads as a 6/12 pitch.
Pitch, angle, and slope factor
The same roof can be described three ways. Pitch is the ratio builders use. The angle, found with arctangent of rise over run, is the degree measure an architect or a solar installer may want. A 6/12 pitch works out to about 26.57 degrees.
The slope factor is the length of the rafter line divided by the run, or the square root of rise squared plus run squared, over the run. It is the multiplier that turns the flat area a roof covers into the larger sloped surface you actually shingle.
Common roof pitches
Low-slope roofs run from about 2/12 to 4/12 and shed water slowly, so they need careful sealing. Conventional house roofs often sit between 4/12 and 8/12, a range that drains well and is still safe to walk with care.
Steep roofs above 9/12 climb past 37 degrees and usually call for staging or fall protection to work on. Knowing the pitch ahead of time tells you what materials suit the roof and how much extra area the slope adds to a shingle order.
Frequently asked questions
- What is a 6/12 roof pitch in degrees?
- A 6/12 pitch rises six inches over a twelve-inch run. Its angle is the arctangent of 6 divided by 12, which is about 26.57 degrees. Its slope factor is roughly 1.118.
- What is the slope factor used for?
- The slope factor converts the flat footprint a roof covers into the actual sloped surface area. Multiply the footprint area by the slope factor to get the area to cover with shingles or other roofing.
- How is roof pitch different from the angle?
- Pitch is a ratio of rise to a 12-unit run, like 6/12, which roofers use. The angle is the same steepness expressed in degrees. The calculator shows both from the same rise and run.
- What is a standard run measurement?
- Run is usually measured over a standard 12 inches, which is why pitch is quoted as a number over 12. The calculator normalizes any run you enter to that 12 base so the ratio reads conventionally.
- What roof pitch is considered steep?
- Pitches above about 9/12, or roughly 37 degrees, are considered steep and usually require staging or fall protection to work on safely. Most house roofs fall between 4/12 and 8/12.