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Bend allowance
calculator.

Start with the part.
Find the flat.

Calculate bend allowance and bend deduction in inches or millimeters. Enter your outside leg dimensions, thickness, inside radius, angle and K-factor to estimate the flat length for one sheet metal bend.

01 / Design for the bend

Calculate bend allowance, deduction and flat length.

Start with your finished dimensions. Find the flat length for a single bend, and see where the material goes.

1 Your finished part

Measure each leg along its outside face to the theoretical sharp corner, where the outside faces would meet. The dotted corner in the drawing shows this point.

Outside leg A

Outside leg B

Angle measured as

Angle

deg

Rotation from a flat sheet. Inside opening: 90°.

Try a bend:

2 Material & bend setup

Thickness · T

Inside radius · R

K-factor

The neutral axis location through the thickness, measured from the inside. Enter your calibrated value from 0 to 0.5.

Have a gauge number? Look up the material in the sheet metal gauge-to-thickness chart, then enter its decimal thickness. Use the ordered thickness and verified bend inputs for production.

The starting radius and K-factor are example values, not material-specific Xeon specifications. Use your shop’s measured bend data for production. Find your material’s catalog radius and K-factor →

Formed profile

OUTSIDE DIMENSIONS

Blue arc: the neutral axis through the bend. Dimensions are in in; the view fits your part.

Unfolded blank

ONE CONTINUOUS SHEET

Bend allowanceDeveloped bend center

Estimated flat blank length

—in

A + B − bend deduction

Bend allowance · BA: — in
Bend deduction · BD: — in
Outside setback: — in
Developed bend center: — in

Single-bend geometry estimate. This does not check tooling clearance, minimum flange length, or springback. Confirm your bend data before cutting; the developed center is not a press-brake backgauge setting.

Why the flat is shorter than A + B

Your outside dimensions include the theoretical corner on both legs. Bend deduction removes that overlap and accounts for the developed bend.

Flat length = A + B − BD

The math behind the result

θ is the bend from flat in degrees. An inside opening of 120° means a 60° bend from flat.

BA = (π / 180) × θ × (R + K × T)
Setback = (R + T) × tan(θ / 2)
BD = 2 × setback − BA

Worked example: a 90-degree bend

For outside legs A = 2 in and B = 2 in, thickness T = 0.063 in, inside radius R = 0.063 in and K = 0.42:

BA = 0.1405 in
Setback = 0.1260 in
BD = 0.1115 in
Flat length = 3.8885 in

Use validated bend inputs

This is an illustrative calculation, not production bend data. The 90-degree angle is measured from flat. Actual radius and K-factor depend on the material and process; confirm them before releasing a flat pattern.

Use the prototyping checklist to connect the flat layout to a finished-part drawing and first-part checks.

More than one bend?
Build the complete profile in our simulator.

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Bend allowance vs. bend deduction: which should I use?

Bend allowance is the developed length through the curved region. Add it to two straight tangent lengths to find the flat length. Bend deduction is subtracted from the sum of two finished outside dimensions measured to the theoretical sharp corner. This calculator takes those outside dimensions, so its flat length is A + B − bend deduction. Do not subtract bend allowance from outside leg lengths.

Use the sheet metal K-factor guide to understand the neutral-axis input, and the bend deduction and allowance charts to review the associated terminology and tooling references.

How should I measure legs A and B?

Use the finished outside dimensions from each free edge to the theoretical sharp intersection of the two outside faces. Do not enter the straight distance to the start of the radius. For straight tangent lengths, the relationship is different: flat length = straight A + bend allowance + straight B.

Which K-factor and radius should I use?

Use measured values or a validated bend table for the material, thickness, tooling, and forming process you will use. A generic material name does not determine either value. The example starts at K = 0.42 so you can explore the calculation; it is not a guarantee for a specific alloy. Read our bending guide ↗

What is the difference between bend angle and inside opening?

A bend from flat measures how far the sheet rotates away from a straight sheet. The inside opening is the angle between the finished legs. They add to 180°. Both are 90° for a right-angle bracket. Switching the angle convention here keeps the same part and converts the number for you.

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