Free tool
Calculate bend radius
The opening of the bend die (V-die) determines which inside bend radius is achievable — and that radius needs to suit the material. Calculate the inside and outside radius below, and see right away if the radius is too tight for the chosen material.
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How do V-die width and radius relate?
With air bending (the common bending process), the punch pushes the sheet into the die's V-opening until the target angle is reached. The inside bend radius follows both from the V-die width and from the punch's own nose radius:
inside radius (ID) ≈ V-die width / 6 outside radius (OD) = inside radius + material thickness recommended punch nose radius ≈ desired inside radius
Prefer to start from a desired radius instead of a V-die? This tool works the same rule of thumb backwards to find the matching V-die width.
Minimum radius per material
A radius that's too tight relative to the thickness can crack or fracture the outer fibre of the bend. As a rule of thumb:
| Material | Minimum inside radius |
|---|---|
| Structural steel (S235/S355) | 1 × thickness |
| Stainless steel 304/316 | 1.5 × thickness |
| Aluminium (5754/6082) | 1 × thickness |
Stainless steel work-hardens more strongly during bending than mild steel, so it typically needs a wider radius. This remains a rule of thumb for a first estimate — the actual limit also depends on the specific alloy and edge quality (deburred or not). For a borderline case, a test bend remains the only certainty.
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