Press Brake Tonnage Calculator
Air-bending force from material, thickness, die opening, and bend length — in kN and tons
Air bending force depends on four things: the material’s tensile strength, the square of the sheet thickness, the die opening, and the bend length. The thickness enters squared — doubling the sheet from 2 to 4 mm quadruples the required tonnage, which is why press capacity runs out faster than intuition suggests.
This calculator uses the standard air-bending formula F = 1.42 × Rm × t² / V and adds the practical numbers around it: the recommended die opening (the 8×t rule), the resulting inner radius (≈ V/6.4), the minimum flange length you can bend on that die (≈ 0.7 × V), and a 20% safety margin for the recommended press size.
Rules of thumb: stainless needs roughly 1.6× the force of mild steel; soft aluminum roughly half. A narrower die reduces the inner radius but increases force and marking; a wider die does the opposite. When in doubt, size the die at 8× thickness and check the flange minimum.
Frequently Asked Questions
How do I calculate press brake tonnage?
For air bending: F (kN/m) = 1.42 × tensile strength (N/mm²) × thickness² (mm) / die opening (mm). Multiply by bend length in meters and divide by 9.81 for metric tons. Example: 2 mm mild steel (420 N/mm²) over a 16 mm die = 149 kN/m ≈ 15.2 t per meter.
What die opening should I use?
The standard rule is V = 8 × thickness for sheets up to ~6 mm (10–12× for thicker plate). A larger V lowers force and enlarges the inner radius; a smaller V does the opposite but risks cracking and needs more tonnage.
How much more force does stainless steel need?
Roughly 50–70% more than mild steel at the same thickness and die, proportional to its higher tensile strength (~680 vs ~420 N/mm²). Aluminum needs roughly half of mild steel.
Does this apply to bottoming and coining?
No — this formula is for air bending, the most common method. Bottoming requires roughly 3–5× more force and coining 5–8× more. If you plan to bottom or coin, multiply accordingly and check your press and tooling ratings.