Find the pitch, angle, and slope of your roof from rise and run measurements.
Step 1: Measure the rise – the vertical height from the top of the wall plate to the ridge.
Step 2: Measure the run – the horizontal distance from the outside wall to directly below the ridge.
Step 3: The calculator returns the pitch as a ratio (X:12 for imperial, or X:1 for metric), the angle in degrees, and slope as a percentage.
The rafter factor tells you how long the rafter is per unit of horizontal run – multiply it by the run to get the rafter length on the slope.
Common roof pitches range from 4:12 to 9:12. A 4:12 pitch (18.4°) is considered low slope, while 9:12 (36.9°) is steep. Most residential roofs fall between 5:12 and 8:12.
Most asphalt shingle manufacturers require a minimum 2:12 pitch (9.5°). Below that, you typically need a membrane or built-up roofing system.
Angle = arctan(rise / run). For a 6:12 pitch: angle = arctan(6/12) = 26.57°.
Most plain and interlocking tiles need at least a 15–22.5° pitch, depending on the tile. Below that you usually need slates rated for low pitch or a different covering.
Pitch affects how well a roof sheds rain and snow, which coverings you can use, and how much material you need — a steeper roof has more surface area to cover.
