Sheet Metal K-Factor Calculator

Calculation mode

Choose calculation

Material and bend geometry

Sheet thickness

Inside bend radius

Dimension unit Bend angle

Bend allowance

Enter the measured or validated bend allowance for the selected bend angle.

Measured neutral axis

Distance from inside surface to neutral axis

This is the measured distance from the inside surface of the bend to the neutral axis.

K-factor

Typical K-factor values are often below 0.50, but actual values depend on material, tooling and bend conditions.

Calculated results

K-factor

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Bend allowance

—

Neutral-axis distance

—

Neutral-axis radius

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Calculation details

Enter your bend data and calculate.

K-Factor Formula

K = (BA ÷ (θ × t)) − (R ÷ t) where: K = K-factor BA = bend allowance θ = bend angle in radians t = material thickness R = inside bend radius Neutral-axis distance = K × t Neutral-axis radius = R + (K × t)

The bend angle must be converted from degrees to radians before using the bend allowance equation.

Example

Material

2 mm sheet with a 3 mm inside radius and a 90° bend.

Bend allowance

7.85 mm.

Calculation

K = [7.85 ÷ (π/2 × 2)] − [3 ÷ 2].

Result

K-factor ≈ 0.50.

Why K-factor matters

It locates the theoretical neutral axis inside the sheet.
It is used when calculating bend allowance.
It helps develop accurate flat patterns.
It varies with material and bending conditions.
It can be determined experimentally from a known bend.
Validated shop data is generally more useful than a generic assumed value.

A calculated K-factor is only as reliable as the bend measurements and bend allowance used. For production work, validate the value using your actual material, tooling, thickness and bending process.

Frequently Asked Questions

What does K-factor mean? K-factor describes where the neutral axis lies through the sheet thickness during bending. It is the neutral-axis distance from the inside surface divided by material thickness.

What is the standard K-factor? There is no single universal K-factor. Values vary according to material, thickness, bend radius, tooling and process.

Can I calculate K-factor from a bend allowance? Yes. Enter sheet thickness, inside radius, bend angle and bend allowance and the calculator derives K-factor.

Can I calculate bend allowance from K-factor? Yes. Select the bend allowance mode and enter the K-factor.

What is the neutral axis? The neutral axis is the theoretical region within the sheet where the longitudinal length remains approximately unchanged during bending.

Why does the bend angle use radians? The bend allowance equation uses arc length, and arc length requires the angle in radians.

Can I use this for production? Use it as an engineering calculation aid. Production values should be validated against your machine, tooling and material-specific bend tests.

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