Roof Pitch Calculator

Calculate roof pitch in degrees and percentage from rise and run measurements. Determine roof type and rafter length.

Roof pitch describes how steeply a roof rises, expressed as the vertical Rise over a horizontal Run -- traditionally 12 inches, so a "6/12" roof rises 6 inches for every foot it runs. This calculator turns that ratio into three other readings framers and inspectors actually use: Pitch (Degrees), computed as the arctangent of Rise divided by Run; Pitch (Percent), the same ratio expressed as a percentage; and a Roof Type classification (Low Slope at a ratio of 0.25 or under, Conventional up to 0.75, Steep beyond that). Both Rise and Run push Pitch (Degrees) in opposite directions -- a taller Rise steepens the angle, while a longer Run flattens it for the same Rise -- but because the default Run (12 inches) is twice the default Rise (6 inches), a proportional change to Run moves the raw Rafter Length output more than the same proportional change to Rise does. Rafter Length here is the straight-line hypotenuse computed directly from whatever Rise and Run you enter (the square root of Rise squared plus Run squared) -- it only reads as "length per foot of horizontal run" when Run is left at the standard 12 inches; changing Run to model a different span turns it into the diagonal for that custom rise-and-run pair instead. The calculator does not account for overhang, hip or valley framing, or the extra length ridge and hip rafters need beyond a simple common rafter.