Roof Pitch Calculator
The roof pitch calculator calculates rise, run, slope, pitch, angle, and rafter length. Use the diagrams as a reference for the Input values, and to interpret the calculated Results.
The roof pitch calculator calculates the following common rafter building scenarios:
- Pitch(X) - (based on Rise and Run)
- Rise(M) - (based on Pitch and Run)
- Run(R) - (based on Rise and Pitch)
In addition to Pitch, Rise, and Run, this rafter calculator is also a Rafter Length Calculator, and a Rafter Angle Calculator.
To determine the finished height of the ridge beam, add the Rise (M) and the Y height. To determine the Y height, measure from the bird's mouth up the calculated slope (X in 12) to the top of the rafter. The top of the ridge beam = M + Y.
The Roof Pitch Calculator Input Options (explained)
Pitch(X) - This option (the default) places the Rise[M] and Run[R] fields into the Input section. The pitch is represented as the number of inches of Rise[M] for every 12 inches of Run[R].
Rise(M) - This option places the Run(R) and Pitch(X) fields into the Input section, and moves the Rise(M) field to the Results section. Select this option if you know the rafter's Run(R) and the roof's Pitch(X), and need to determine the Rise(M) of the rafter.
Run(R) - This option places the Rise(M) and Pitch(X) fields into the Input section, and moves the Run(R) field to the Results section. Select this option if you know the rafter's Rise(M) and the roof's Pitch(X), and need to determine the Run(R) of the rafter.
Roof Pitch Chart
This roof pitch chart provides a visual representation of the actual pitch(X)/angle(A) of a roof.
Roof Pitch Chart
Roof Pitch Calculator Results Explained
Pitch/Slope - Pitch and slope, often used interchangeably on the job site, refer to a roof's slope represented as X in 12, where X is the number of inches of rise for every 12 inches of run. Roof slope information is used for laying out rafters with a Framing Square. The roof pitch calibrations on a Speed Square are also used for quickly marking the pitch cut angles on the head and tail ends of rafters.
Angle - The angle of a roof is the same as the roof's slope, except instead of being represented as X in 12, it is represented in degrees. The angle information is valuable when you are performing roof framing tasks using tools that are not roof-pitch calibrated, such as the bevel on a circular saw, which is calibrated in degrees.
Rafter Length - The rafter length results, from this calculator, represents the length of line L on the diagram(s). Note that this is not the actual length of the rafter. It is the length of this portion of the rafter. If you plan to have overhang, etc., the overall rafter material will be longer.
Rafter Length Calculator
Note: If you are calculating rafter length from the center of the ridge beam, you will need to subtract half of the thickness of the ridge beam from the top end of the rafter. For example, if the ridge beam is 1 1/2 inches thick, subtract 3/4 of an inch, perpendicularly, from the upper pitch cut, resulting in a new upper pitch cut parallel to the first.
Roof Pitch Diagram
Roof Pitch Calculator - Related Links
To determine maximum rafter spans, visit the Rafter Span Tables page on mycarpentry.com.
For more information on roof building, cutting rafters and other design considerations, visit mycarpentry's Roof Framing section.