Angle: 26.57 degrees
Slope: 50%
Rafter length: 13.42
Run used: 12
How to use this roof pitch calculator
Enter the rise and the run in the same unit, inches or feet. Rise is how far the roof climbs vertically, and run is the horizontal distance from the wall to the ridge. If you know the full span instead of the run, switch to Rise and Span: the run is half the span, so a 24 foot span means a 12 foot run. The calculator shows the pitch, the angle in degrees, the slope as a percent, and the rafter length in the same unit you entered.
How roof pitch works
Roof pitch is the rise divided by the run, times 12, and it is written as X over 12. A rise of 6 with a run of 12 gives 6 divided by 12 times 12, which is a 6/12 pitch. The angle is the arctangent of rise divided by run: for 6 over 12 that is 26.57 degrees. The slope is rise divided by run as a percent, so 6 over 12 is a 50 percent slope. The rafter length comes from Pythagoras: the square root of rise squared plus run squared. For a rise of 6 and a run of 12, the square root of 36 plus 144 is the square root of 180, which is 13.42.
Common roof pitch examples (per 12 of run)
| Pitch | Angle | Slope | Rafter length |
|---|---|---|---|
| 4/12 | 18.43 degrees | 33.33% | 12.65 |
| 6/12 | 26.57 degrees | 50% | 13.42 |
| 8/12 | 33.69 degrees | 66.67% | 14.42 |
| 12/12 | 45 degrees | 100% | 16.97 |
Frequently asked questions
What does a 6/12 roof pitch mean?
A 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal run. The angle is 26.57 degrees and the slope is 50 percent.
How do I calculate roof pitch?
Divide the rise by the run and multiply by 12. A rise of 6 with a run of 12 is 6 divided by 12 times 12, which is a 6/12 pitch.
What is the difference between roof pitch and slope?
Pitch is written as X over 12, while slope is the same ratio as a percent. A 6/12 pitch is a 50 percent slope, and a 12/12 pitch is a 100 percent slope.
What is a normal roof pitch?
Most US homes use a pitch between 4/12 and 9/12. Below 4/12 is low-slope and needs special roofing material. Above 9/12 is steep and harder to walk on.
How do I find the rafter length?
Use Pythagoras with the rise and run: rafter length is the square root of rise squared plus run squared. For a rise of 6 and a run of 12, that is the square root of 180, which is 13.42 in the same unit as your measurements.