What is bend allowance?

Bend allowance is the length of material along the neutral axis consumed by a bend. It helps estimate the flat pattern length before press brake forming.

Is the calculator a substitute for shop bend tables?

No. Use it for planning and RFQ conversations. Final bend deductions depend on material, thickness, tooling, grain direction, bend radius, and FortiFab shop review.

What K-factor should I use?

A common planning range is 0.30–0.45. Thicker material, sharper bends, tooling, and process conditions can move the real neutral axis, so confirm final values before release.

Bend allowance calculator

Estimate sheet metal flat length before press brake forming

Calculate bend allowance, outside setback, bend deduction, and a planning flat length from thickness, inside radius, bend angle, K-factor, and flange lengths. FortiFab uses this kind of information to make quote reviews faster and cleaner.

Inputs

Material thickness (in)

Inside radius (in)

Bend angle (degrees)

K-factor

Outside flange A (in)

Outside flange B (in)

Bend allowance

0.125 in

Outside setback

0.120 in

Bend deduction

0.115 in

Flat length

3.885 in

Formula used

Bend allowance = angle in radians × (inside radius + K-factor × material thickness). For a single bend with outside flange dimensions, bend deduction = 2 × outside setback − bend allowance.

BA = A × (R + K × T)
OSSB = tan(A / 2) × (R + T)
BD = 2 × OSSB − BA
Flat length = flange A + flange B − BD

These values are planning estimates. Final production values depend on material, tooling, grain direction, bend method, and tolerance stack-up.

Need FortiFab to review the part?

Send your DXF, STEP, or drawing package with material, finish, and quantity. We will confirm manufacturability before production.

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Bend allowance FAQs

Planning notes for sheet-metal bend allowance, K-factor, and flat-pattern estimates.