90 degree bends: Multiply the radius of the bend by 1.57 (Radius is measured to the center of the pipe) To find the length of a 90-degree bend. 180 degree bends: Multiply the radius of the bend by 3.14 to find the length of a 180-degree bend.It is possible to have a tighter bend radius, even as low as ½ x D, although anything below 2 x D will usually require costly tooling and probably mandrel bending.