Explanation of how to convert rise/run to roof pitch angle.

1. What is the pitch angle of a
2/12 roof?
SolPowerPeople, Inc.
Austin, TX
March 6, 2012

2. First we must understand what
2/12 means?

3. It refers to the rise over the run
2”
12”

4. For every 2” of rise, there is
12” of run
2”
12”

5. So how do we solve for the
angle?
2”
?°
12”

6. We know that the tangent of
the angle is equal to the
opposite over the adjacent
opposite
Opposite
tan(q )° =
adjacent
2”
?°
12”
Adjacent

7. Therefore, 2 divided by 12 is
the tangent of the angle which
is 0.1666
Opposite
2”
?°
12”
Adjacent

8. How to solve
In order to convert from the tangent of an angle to
Opposite the actual angle value use the arctan function
2”
?°
12”
Adjacent

9. Arctan function
Press shift
or 2nd key

10. Arctan function
Press Arctan key
(i.e. tan-1 key)

11. Arctan function
Answer: 2/12 pitch
roof has a pitch
angle of 9.46°