// Free Engineering Tool

Bend Allowance & Flat Pattern Calculator

Calculate bend allowance, bend deduction and flat pattern length for sheet metal bends. Choose material for a typical K-factor (or set your own), enter thickness, inside radius and bend angle, and get the flat blank size instantly by both the bend-allowance and bend-deduction methods — with a table of allowance across bend angles. Verified against standard fabrication formulae.

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Bend & Material

Material (K-factor)

Material Thickness

K-Factor

Inside Bend Radius

Bend Angle

Leg A

Leg B

Leg A & B are the flat flange lengths to the bend tangent line (BA method).

Bend Allowance BA = (π/180)·A·(R + K·T). Bend Deduction BD = 2·OSSB − BA, where OSSB = tan(A/2)·(R+T). Flat length: legs measured to the bend tangent, plus BA; or outside dimensions minus BD. K-factor is material-dependent — verify with a test bend for critical work.

Results

Flat Length (BA method)—

Bend Allowance—

Bend Deduction—

Outside Setback—

Neutral Axis Offset—

Bend Allowance vs Angle — Current Material

Angle	BA	BD	OSSB

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