Calculators / Bend allowance

Bend allowance

Enter material thickness, bend angle, inside radius, and K-factor to get bend allowance, bend deduction, setback, and the flat pattern length for a single bend with two flanges.

Inputs

All dimensions in the same unit (inches or millimeters). Results come back in that unit.

Material thickness (T)

Inside bend radius (R)

Bend angle (degrees from flat)

K-factor

Flange 1 length (outside)

Flange 2 length (outside)

Flat pattern length2.896

Bend allowance (BA)0.136

Bend deduction (BD)0.104

Setback (SB)0.120

Neutral axis offset (K x T)0.026

K-factor starting points: 0.33 for a sharp coined bend, 0.42 to 0.44 for typical air bending of mild steel, up to 0.50 as radius grows past 2x thickness. Your press brake shop can give you measured values for their tooling, which always beat theory.

Visual reference

A single bend, viewed from the end. Flange lengths are measured to the outside mold line.

Formulas used

Bend allowanceBA = A(rad) x (R + K x T)

SetbackSB = tan(A / 2) x (R + T)

Bend deductionBD = 2 x SB - BA

Flat patternFlat = Flange 1 + Flange 2 - BD

This tool covers a single bend up to 180 degrees with flanges measured to the outside mold line. For parts with multiple bends, subtract one bend deduction per bend from the sum of all outside dimensions.