Roof Pitch Calculator
Convert roof pitch between rise-over-run (x/12), degrees, and slope factor. Calculate rafter length from the run and pitch for any roof.
Pitch
6/12
Angle
26.57°
Slope Factor
×1.1180
multiply by run for rafter
Rafter Length
13.42 ft
excl. overhang
Rafter length excludes overhang — measure your eave overhang separately and add it to the rafter length.
Reverse: angle → rise/12
Have a pitch angle in degrees? Find the equivalent rise per 12 inches.
Rise per 12"
6.00/12
Frequently Asked Questions
What does a 6/12 roof pitch mean?
A 6/12 pitch means the roof rises 6 inches vertically for every 12 inches of horizontal run. The first number is always the rise and the second is always 12 (the standard run base). A 6/12 pitch is considered moderate — common on many residential homes. Steeper pitches (8/12, 10/12) shed water faster but are harder to walk on; low pitches (2/12, 3/12) need special underlayment to prevent leaks.
How do I convert roof pitch to degrees?
Use inverse tangent (arctan): angle = arctan(rise ÷ 12). For a 6/12 pitch: arctan(6/12) ≈ 26.57°. A 12/12 pitch equals exactly 45°. The reverse works too — if you have an angle in degrees, the equivalent rise per 12 is: rise = tan(angle) × 12.
How do I calculate rafter length from pitch?
First find the slope factor: √(rise² + 12²) ÷ 12. For a 6/12 pitch the slope factor is √(36+144)/12 ≈ 1.118. Multiply the slope factor by the horizontal run (ridge to wall) to get rafter length. A 12-foot run at 6/12 pitch yields about 13.42 feet of rafter — not counting any overhang, which you add separately.