Roof pitch calculator
Measure the rise over a known horizontal run, like 12 inches. You’ll get the pitch, angle and rafter length.
Roof pitch
6/12
- Angle
- 26.57 degrees
- Slope
- 50 %
- Pitch multiplier
- 1.118 × horizontal run
- Rafter length
- 13 ft 5 in before overhang
How it works
Pitch is how many inches a roof rises for every 12 inches of horizontal run. The calculator scales your rise and run to a run of 12. The angle is the arctangent of rise ÷ run, and the pitch multiplier, √(1 + (rise ÷ run)²), turns any horizontal distance into the sloped distance along the roof.
Example
With rise 6 in, run 12 in, the answer is 6/12 .
Tips before you buy
- To measure from the attic, hold a level horizontally against a rafter, mark 12 inches along the level, and measure straight up to the rafter.
- Most asphalt shingles need a pitch of at least 2/12 with extra underlayment, and 4/12 or more for standard installation. Check the shingle wrapper.
- Add the overhang to the rafter length, and measure along the slope for the overhang too.
Common questions
What angle is a 6/12 roof pitch?
26.57 degrees.
What angle is a 4/12 pitch?
18.43 degrees. A 12/12 pitch is 45 degrees.
What is a common roof pitch?
Between 4/12 and 9/12 is common for houses. Lower pitches drain more slowly and limit roofing choices.