Roof Pitch Calculator
The roof pitch calculator calculates rise, run, slope, pitch, angle, and rafter length. Use the diagrams on this page when referring to the Input section 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 Roof Pitch 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 inside of the Birdsmouth up the calculated Pitch (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(X/12) represents 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 of the calculator 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) 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
The roof pitch chart is a visual representation of the actual slope of a roof, given the roof's Pitch(X)/Angle(A).
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 Pitch(X) represented as X in 12, where X is the number of inches of vertical rise for every 12 inches of horizontal run. If you know a roof's Pitch(X), you can use the information to lay 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 - Angle(A) is the roof's Pitch(X) represented in degrees. The angle information is valuable when performing roof framing tasks using tools that are not roof-pitch calibrated, such as the Bevel on a circular saw, which is degrees calibrated.
Rafter Length - The rafter length result from this calculator represents the Line Length of the Rafter(L). Note that this is not the actual end-to-end length of the rafter. It is the length of a line beginning at the inside of the Birdsmouth drawn parallel to the edge of the rafter. If you plan to have an overhang on your rafter tails, the rafter length will be longer. It is common practice to install rafters with the ends running long, then cut them later.
Rafter Length Calculator
If you are calculating the 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 from the upper pitch cut, resulting in a new upper pitch cut parallel to the first.
Roof Pitch Diagram
Roof Pitch Calculator - Related Links
Rafter Span Tables - Determine maximum rafter spans for different species of lumber.
Roof Framing - How to design and build Shed and Gable roofs.
Carpentry Squares - Framing Squares and Speed Squares for roof framing.