Work out k factor for bending instantly with clear inputs, formula shown and shareable results.
K-factor is derived by working the bend allowance formula backwards. Dividing measured allowance by the bend angle in radians gives the neutral axis radius; subtracting the inside radius and dividing by thickness gives K as the fraction of thickness at which the neutral axis sits. The Y-factor used by some CAD systems is simply K times pi over two.
K-factor
K = (BA / angle in radians - R) / T
Y-factor
Y = K x pi / 2
K = (BA / angle in radians - R) / T. K-factor is derived by working the bend allowance formula backwards.
Bend a test piece, measure the two outside flanges and the overall flat length, then BA = flat length - (flange A + flange B - 2 x setback). One test per material and tooling combination is enough.
This calculator takes 4 inputs: Measured bend allowance, Bend angle, Inside bend radius, Material thickness. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.