Bend Allowance Calculator
Calculate the exact flat length needed before bending sheet metal, accounting for material thickness, bend radius, and angle.
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Tips for Accurate Bending
Use Correct K-Factor
The K-factor (typically 0.3–0.5) depends on material, bend radius, and thickness. Default of 0.44 works for most mild steel at common radii.
Account for Springback
Materials spring back after bending. Over-bend by 2–3° for steel and up to 6° for aluminum to achieve the target angle.
Measure Bend Radius Accurately
Bend radius is measured to the inside of the bend. Use the punch tip radius for press brake work.
Test Before Production
Always make test bends to verify your calculations before cutting a full production batch.
Frequently Asked Questions
What is bend allowance?
Bend allowance is the length of material consumed in the bend zone. It equals the flat length needed before bending to achieve the desired final dimensions after bending.
How do I calculate bend allowance?
Formula: BA = (π/180) × (R + K × T) × A, where R = bend radius, K = K-factor (0.3–0.5), T = material thickness, A = bend angle in degrees.
What is the K-factor in sheet metal bending?
The K-factor is the ratio of the neutral axis distance to material thickness. It typically ranges from 0.3 to 0.5, with 0.44 being a common starting point for mild steel.
Why does my bent part come out wrong?
Common causes: incorrect K-factor, not accounting for springback, wrong bend radius, or inconsistent material thickness. Always test with a sample piece first.
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