Sheet Metal Bending Allowance Calculator
Calculate bend allowance, bend deduction, and neutral radius for sheet metal bending operations using the K-Factor method.
Results
What is it?
When sheet metal is bent, the inner surface compresses and the outer surface stretches. The neutral axis is the layer that neither compresses nor stretches. Bend allowance (BA) is the arc length of material consumed by the bend along the neutral axis. Bend deduction (BD) is the shortening applied to the flat blank length to account for the bend.
How to use
Enter the bend angle (interior/included angle), material thickness, inside bend radius, and K-Factor. Use the Bend Allowance to calculate flat pattern length: Flat Length = Leg 1 + Leg 2 + Bend Allowance. Use Bend Deduction: Flat Length = Leg 1 + Leg 2 รขหโ Bend Deduction (where legs are measured to the outside mold lines).
Example scenario
Bending 2 mm mild steel at 90รยฐ with a 2 mm inside radius and K-Factor 0.33. Neutral Radius = 2 + 0.33 รโ 2 = 2.66 mm. Bend Allowance = (รโฌ/2) รโ 2.66 = 4.18 mm. For a part with two 50 mm legs, flat blank = 50 + 50 + 4.18 = 104.18 mm.
Pro tip
K-Factor varies with material, tooling, and bend radius-to-thickness ratio. Tight bends (IR < 1รโ t) require a lower K-Factor (0.28รขโฌโ0.33); air bending large radii can reach 0.42รขโฌโ0.45. Always validate your K-Factor against a test bend on the actual material and press brake tooling before cutting production blanks.