Sheet Metal Bend Allowance Calculator by Material

Material

Select material

Material and bend dimensions

Sheet thickness

Inside bend radius

Dimension unit

Bend angle

K-factor

Calculated Results

Bend allowance

—

K-factor used

—

Neutral-axis radius

—

Neutral-axis distance

—

Calculation Details

Enter your material and bend data.

Material K-Factor Reference

Mild Steel

Suggested starting K-factor: 0.40

Stainless Steel

Suggested starting K-factor: 0.42

Aluminum

Suggested starting K-factor: 0.40

Galvanized Steel

Suggested starting K-factor: 0.40

Copper

Suggested starting K-factor: 0.45

Brass

Suggested starting K-factor: 0.42

Titanium

Suggested starting K-factor: 0.45

These are starting estimates, not universal material constants. Actual K-factor varies with material grade, temper, thickness, radius, tooling and bending method.

Formula

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

The selected material provides a starting K-factor. You can override it with your own validated K-factor when the Custom K-factor option is selected.

Example

Mild steel

2 mm thickness, 3 mm inside radius, 90° bend and K-factor 0.40.

Neutral-axis radius

3 + (0.40 × 2) = 3.8 mm.

Bend allowance

π/2 × 3.8 ≈ 5.97 mm.

Frequently Asked Questions

What is bend allowance? Bend allowance is the length of material along the neutral axis that forms the bend.

Why calculate bend allowance by material? Different materials and forming conditions can produce different neutral-axis behavior, so material-specific data can improve flat-pattern calculations.

Is there one K-factor for each material? No. The values in this calculator are starting estimates. Actual K-factor depends on material and manufacturing conditions.

Can I enter my own K-factor? Yes. Select Custom K-factor and enter your validated value.

Why is bend angle converted to radians? Because bend allowance is the arc length of the neutral-axis curve, and arc-length calculations use radians.

Does inside radius affect bend allowance? Yes. Increasing the inside radius increases the neutral-axis radius and therefore increases bend allowance.

Does sheet thickness affect bend allowance? Yes. Thickness affects the neutral-axis position through the K-factor term.

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