Online Tool Store
Bend Allowance Calculator
Bend Allowance Calculator gets the flat pattern close; the test piece is what accounts for springback and tooling. Runs entirely in your browser with no upload.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Math & Science
Bend Allowance Calculator
Frontend preview — no upload or external service.
Flat length
Flat length: 132.8 mm. Bend allowance for this 2 mm material is 2.8 mm per 90° bend.
How the Bend Allowance Calculator works
- Measure material thickness and confirm the tooling's inside bend radius.
- Use a K-factor appropriate to the material and process — it is the largest source of error and varies with both.
- Cut a test piece before committing a batch. Calculated flat lengths get you close; the test piece gets you right.
The method
Material on the outside of a bend stretches and the inside compresses. The neutral axis, where neither happens, sits at a fraction of thickness called the K-factor.
BA = angle(rad) x (radius + K x thickness)
K typically falls between about 0.33 and 0.5 depending on material and forming method, and that range shifts the flat length enough to matter.
FAQ
What is the K-factor?
The position of the neutral axis as a fraction of material thickness. It shifts with material, thickness and forming method, and it is the number that determines whether your flat pattern is right.
Why does my part come out the wrong size?
Usually the K-factor, the actual inside radius differing from the assumed one, or springback. Air bending in particular produces a radius set by the die opening rather than the punch.
Do I still need a test piece?
Yes. Calculation gets you close; material batch variation, tooling wear and springback account for the rest. One test piece before a production run is always cheaper than the run.
How we compare
| Feature | Online Tool Store | A graphing calculator | A stats package |
|---|---|---|---|
| Bend allowance and deduction | ✓ | One | ✓ |
| Configurable K-factor | ✓ | ✗ | ✓ |
| No sign-up | ✓ | ✓ | ✗ |
| Nothing uploaded | ✓ | ✗ | ✗ |
Bend Allowance Calculator gets the flat pattern close; the test piece is what accounts for springback and tooling.