Press Brake Tonnage Calculator
Press brake tonnage depends on material strength, thickness squared, bend length and the width of the V die. This calculator estimates the force for air bending, bottoming or coining and compares it with the capacity of your machine.
Your numbers
Use the mill certificate value for the actual lot if you have it.
A common starting rule for air bending is 6 to 8 times the thickness.
Multipliers are rule-of-thumb values. Check the tooling maker's chart for exact numbers.
Your results
This is an estimate based on the common air bending formula. Always confirm against the press manufacturer's and tooling maker's load charts, and never exceed the lowest rated capacity of the punch, die or machine.
Tonnage vs thickness (V die held constant)
Sweeps Thickness from 0.5 to 6, holding your other inputs fixed.
Tie tooling and press data to your routings
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How to use the calculator
Pick a material strength, enter the thickness, V die opening and bend length, and choose the bending method. The tool gives the force in kilonewtons, metric tonnes-force and US short tons, plus tonnes per meter and machine utilization. If utilization approaches or exceeds your safe working range, use a wider V die, bend in sections, use a lower-strength material option, or choose a larger machine. The chart shows how steeply tonnage rises as thickness increases.
- Use the real bend length in contact with the die, not the sheet width.
- Choose the V opening before anything else, since force falls as the V widens.
- Check tooling limits as well as machine capacity.
The formula and its limits
For air bending the common formula is F (kN) = 1.42 x UTS (MPa) x L (mm) x T squared (mm) / (V (mm) x 1000), where V is the die opening. Thickness is squared, so doubling thickness roughly quadruples the force. Narrowing the V raises force and tightens the radius. Bottoming and coining need substantially more, and the multipliers here are rough guides. The result also varies with yield behavior, die radius, friction and sheet condition, so treat it as a planning estimate.
- Force scales with thickness squared.
- Force falls in inverse proportion to V width.
- Tooling manufacturers publish their own load limits per meter.
Worked example
For 2 mm mild steel at 400 MPa, a 16 mm V die and a 1,000 mm bend, force is about 142 kN, which is roughly 14.5 tonnes. On a 100 tonne press that is about 14.5 percent utilization, comfortable for the machine, though the tooling rating per meter must still be checked. The approximate minimum flange for that V is about 11 mm. For 6 mm plate on the same V, thickness squared is nine times larger, so you would move to a V near 48 mm.
- Check the stroke and daylight for deep parts.
- Check that the punch is rated for the load per meter.
Common mistakes
Using nominal thickness instead of measured thickness, forgetting that stainless and high-strength steels need much more force than mild steel, and choosing a V that is too narrow are the usual causes of overloaded tooling. Another is loading a short part at one end of a long machine, which concentrates force in a small area. Record the V die used for every job in the routing so that quoting, scheduling and the operator all work from the same tooling assumptions.
- Do not load short bends at the table edge.
- Do not exceed the tooling limit even if the machine can.
Frequently Asked Questions
How many tonnes does a press brake need for 2 mm mild steel?
With a 16 mm V die and mild steel near 400 MPa, expect roughly 14 to 15 tonnes per meter for air bending, based on the standard formula. Actual numbers vary with the die, material lot and radius, so check the tooling chart.
What V die opening should I use?
For air bending, a V of about 6 to 8 times the material thickness is a common starting point, with wider openings for thicker plate. A wider V lowers force and gives a larger radius, but also raises the minimum flange length.
Why does stainless need more tonnage?
Because the formula scales with tensile strength. Stainless 304 is commonly around 50 percent stronger than mild steel in this calculation, so the same bend takes proportionally more force. It also springs back more, so overbending is typically needed.
Is this safe to rely on for tooling limits?
No. It is a planning estimate. The rated load of the punch and die, usually given in tonnes per meter, and the machine plate must be checked in the manufacturer's documentation before running a job.
If routing data, tooling lists and press capacity live in different places, Netray can help bring them together inside your ERP. We can build this on private infrastructure.
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