Answer by
esteban (1334)

If A is the angle of the roof, then the formula is tan(A) = rise/run, and equivalently, Arctan(rise/run) = A. For example, with a pitch of 7/12, we have: Arctan(7/12) = 30.25 degrees. And for an angle of 45 degrees, we have: tan(45) = 1 = 12/12.