Calculate the flat blank length for a sheet metal bend, using material thickness, inside radius, and K-factor.
1. Bending Parameters
Enter your flange lengths, bend specs, and K-factor to get the flat pattern length.
Total Flat Blank Length
0.0000 in
Bend Allowance (BA)
0.0000 in
Outside Setback (OSSB)
0.0000 in
Bend Deduction (BD)
0.0000 in
How Bend Allowance Works
When sheet metal bends, the outside stretches and the inside compresses. Somewhere in between sits the neutral axis, the layer that doesn't change length, and the K-factor describes where that layer sits relative to the material thickness. Bend allowance uses that to figure out how much material the bend itself consumes, so the flat blank comes out the right total length. × (π / 180) × (R + K × T). Outside Setback (OSSB) tracking establishes the distance from the intersection of the flat planes to the edge tangent point, while Bend Deduction (BD) parameters reconcile final blank dimensions via a basic deduction matrix (BD = 2 × OSSB - BA).
Worked Example
A 0.060 inch thick sheet bent 90 degrees with a 0.125 inch inside radius and a K-factor of 0.33 needs a bend allowance of 0.2275 inches, giving a flat blank length of 4.8575 inches for 2" and 3" flange legs.
Common Mistakes
Using a generic K-factor for every material and thickness, when it actually varies by alloy, temper, and bend radius.
Confusing bend allowance with bend deduction; they solve related but different problems in flat pattern layout.
Forgetting tighter inside radii increase cracking risk on some materials; this calculator doesn't check minimum bend radius.
Frequently Asked Questions
What is a K-factor?
A ratio describing where the neutral axis sits within the material thickness during a bend, used to calculate how much material the bend consumes.
Is one K-factor always right to use?
No. 0.33 to 0.44 are common defaults, but real K-factors shift with material type, thickness, and bend radius. Check your material supplier's data when precision matters.
What's the difference between bend allowance and bend deduction?
Bend allowance is the material length consumed by the bend itself; bend deduction is what to subtract from the sum of the flange lengths to get the flat pattern. They're two routes to the same answer.
Disclaimer: This tool is provided for educational and informational tracking purposes only. Material deformation metrics provide ideal calculations. Real-world metal behaviors differ widely based on roll directional grains, specific metallurgical tempers, bottoming or air-bend die width tooling configurations, and machinery calibration metrics. Component cut paths must be physically cross-checked and run against raw material testing tabs by qualified press brake operators before initiating industrial blank stamping operations. The website owner assumes no liability.