Sheet Metal Bend Allowance Calculator

Calculate bend allowance using bend angle, radius and K-factor.

Live concept view — geometry scales with the entered design condition.

Calculation paused

Enter valid positive inputs to produce a traceable preliminary result.

Sheet Metal Bend Allowance Calculator: operating questions

Is K-factor a universal material property?

No. It depends on material condition, thickness, bend radius, tooling, grain direction and process. Production bend coupons or approved shop data should control released flat patterns.

Why does bend allowance differ from bend deduction?

Allowance is neutral-axis arc length. Deduction converts outside flange dimensions to developed length and also includes the geometric setbacks. They are related but not interchangeable.

Does this result include springback?

No. Springback affects the over-bend required to obtain the target angle, whereas this simple model calculates neutral-axis developed length from the entered finished geometry.

Illustrative input values and units
Parameter	Unit	Example
Sheet thickness	mm	2
Inside bend radius	mm	3
Bend angle	degrees	90
Validated K-factor	ratio	0.33 (example-only assumption)

Technical verification

Equation checked: 2026-09-15 · Units checked: 2026-09-15 · Independent numerical case: Pass

Source basis: MANUFACTURER DATA — Autodesk Inventor, Sheet Metal Unfold Reference

Unit basis: θ degrees × π/180 → radians; R and t in mm

Independent example: Example-only K=0.33, t=2 mm, R=3 mm, bend angle 90°: BA = 5.74911 mm.

Scope: K is controlled process information, not a universal material property. Use approved shop data, bend coupons or a validated bend table.

Technical verification is not professional engineering certification and does not approve a specific real-world design.