Bend Deduction & K-Factor Calculator

Enter material, thickness, bend angle from flat, inside radius, and outer flange lengths to get K-factor, bend allowance, outside setback, bend deduction, and flat blank length.

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Sheet metal tools for bend layouts

Shears, snips, and gauges that support press-brake flat patterns

Top Pick

Malco TS1 Turbo Shear

Fast blanks from flat stock
Pairs with BD flat pattern cuts
Drill attachment for shop shears

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Radius

SS Radius Gauge Set

Confirm inside bend radius
Critical input for BA / BD
Check formed parts vs print

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Measure

Starrett Digital Caliper

Verify thickness and flange lengths
Check developed blank after bend
Shop metrology staple

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Bend deduction and K-factor formulas

This page focuses on the BD / K-factor workflow fabricators search for. Bend angle A is the angle from flat (90° for a right-angle flange), not the complement.

BA = (π/180) × A × (R + K × T)
OSSB = (R + T) × tan(A × π/360)
BD = 2 × OSSB − BA
Flat = L1 + L2 − BD

K-factor locates the neutral axis through the thickness (0 = inside, 1 = outside). Soft aluminum often uses a lower K than mild steel. Always prove K and BD on scrap with your die and punch set.

Also see the Bend Allowance Calculator for a BA-first workflow on the same geometry.

Diagnose Failures & Choose BA vs BD

Finished dims wrong, cracks, springback, or short flanges: Sheet Metal Bending Troubleshooting. Additive vs subtractive flat-pattern method: Bend Allowance vs Bend Deduction — Which to Use.

Frequently asked questions

When do I use BD vs BA?

Use BD when both flange lengths are outside dimensions. Use BA when you add the arc to the flange flats measured to the mold lines.

Bend Deduction & K-Factor Calculator