🏠 Roof Pitch Calculator
Enter the rise and run of your roof to find its pitch, angle in degrees, and the rafter length needed to span it.
How Roof Pitch Is Calculated
Roof pitch is traditionally expressed as the number of inches a roof rises for every 12 inches of horizontal run, written as X:12 (for example, a 6:12 pitch rises 6 inches for every foot of run). This calculator takes your actual rise and run measurements, scales them to a 12-inch run, and reports the pitch in that familiar X:12 format.
Angle and Rafter Length
The pitch is also converted to degrees using the arctangent of rise divided by run (angle = atan(rise/run)), which is useful for setting a speed square or miter saw. If you provide the total horizontal span of the roof, the calculator estimates the rafter length per side using the Pythagorean relationship between rise, run, and slope distance — the actual hypotenuse a rafter must cover.
Notes
- Rafter length here is a straight-line estimate; actual cut lengths should account for overhang, ridge board thickness, and birdsmouth cuts.
- Steeper pitches (above roughly 9:12) shed water and snow faster but require more roofing material and steeper safe-working precautions.
This tool is for general planning and educational purposes — consult a licensed contractor for structural framing decisions.