Press Brake Tonnage Calculator

Because bending force is proportional to the material's section modulus, which for a rectangular cross-section scales with thickness squared, not thickness itself. The formula this calculator uses reflects that directly -- thickness appears squared in the numerator. Practically, this means thickness is the single most sensitive input: a small increase in material thickness demands a disproportionately larger press brake, which is why tonnage charts for thick plate look so different from those for thin sheet.

Because a wider V-die gives the material more unsupported span to flex across before it contacts the die shoulders, which reduces the bending moment (and therefore the force) needed to form the same bend angle. This is why die opening sits in the denominator of the tonnage formula -- doubling the die opening roughly halves the required force. It's also why the standard 8x-material-thickness die-opening rule exists: too narrow a die forces the material to bottom out (requiring dramatically more force, closer to coining than true air bending) before reaching the target angle.

Because the raw formula result is a theoretical minimum that assumes a fixed tensile strength, frictionless tooling, and a static press. Real material varies in tensile strength between mill heats even within the same nominal grade, tooling friction adds real resistance, and a press brake's usable tonnage can drop as ram speed increases. Sizing a machine to exactly the bare calculated force leaves no margin for any of that variation, so the 20% buffer here is a widely used shop-floor practice, not an arbitrary padding.

This calculator estimates it as roughly die opening divided by 6, a common air-bending rule of thumb: a wider die produces a larger, gentler inside radius because the material has more room to curve across the die's shoulders before the punch forms the final angle. A narrower die forces a tighter radius. This is an approximation for planning purposes -- actual achievable radius also depends on the specific punch nose radius and the material's springback behavior.