Press Brake Tonnage Calculator
This press brake tonnage calculator finds the force needed to air bend sheet metal and plate. Enter the thickness, the bend length, the V-die opening, and the material, and the press brake tonnage calculator returns the bending force in tonnes, kN, and US tons, the force per meter and per foot, the inside bend radius, the minimum flange length, and the press capacity to choose with a safety reserve.
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The Press Brake Tonnage Calculator is part of our Dimensions collection. Browse more dimensions to size, convert, and check your work alongside this tool.
What the press brake tonnage calculator does
In air bending the punch pushes the sheet into a V-die without bottoming out, and the force needed depends on four things: the tensile strength of the material, the thickness squared, the bend length, and the width of the V-die opening. Thicker sheet takes far more force, because thickness is squared, while a wider die lowers the force but makes a larger radius. The press brake tonnage calculator applies the standard air bending formula and adds the die and flange checks a press operator needs before setting up a job.
Press brake tonnage formula
The calculator uses the air bending formula used on most press brake tonnage charts:
UTS is the ultimate tensile strength in MPa, t the thickness and V the die opening in millimeters. The factor 1.42 accounts for friction and the die geometry at a die opening of about 8 times the thickness. One tonne-force is 9.807 kN and one US ton is 8.896 kN. Bottoming takes about 5 times the air bending force and coining about 10 times. The inside radius in air bending forms at roughly 16% of the die opening for mild steel, about 21% for stainless, and 14% for soft aluminum, and the shortest flange that still spans the die is about 0.7 times the opening.
Press brake tonnage calculator example
A 2 m long bend in 3 mm mild steel (450 MPa) on a 24 mm V-die:
With a 20% reserve, a press of at least 61.1 t suits the job. The same 3 mm sheet in stainless 304 needs about 1.44 times the force. A 1.5 m bend in 2 mm stainless on a 16 mm die needs 35.3 t.
How to use the press brake force calculator
Enter the sheet thickness and the bend length in millimeters. Leave the V-die opening at 0 to use the common rule of 8 times the thickness, or enter the die you have. Choose the material, or pick custom and enter the tensile strength from the mill certificate. Keep air bending unless you bottom or coin the part. Press Calculate to read the required force and the press capacity with a 20% reserve.
Reading the bending tonnage result
Compare the total with the rated capacity of the press, and check that the force per meter stays within the rating of the punch and die, which is often stamped on the tool. A bend shorter than the full bed concentrates the load, so many machines limit the force on short parts; follow the machine maker's off-center and short-bend limits. If the force is close to the limit, a wider V-die cuts the tonnage, at the cost of a larger inside radius and a longer minimum flange.
When to use a bending force calculator
- Checking whether a press brake can bend a new part
- Choosing the V-die opening for a thickness
- Quoting sheet metal bending jobs
- Comparing steel, stainless, and aluminum parts
- Planning short bends that load only part of the bed
Common press brake tonnage calculator mistakes
- Using yield strength instead of tensile strength. The formula uses the ultimate tensile strength.
- Forgetting that thickness is squared. Double the thickness needs four times the force.
- Ignoring the tool rating. Check the force per meter on the punch and die.
- Bending across the grain limits. Hard alloys can crack on tight radii.
Tips for using a press brake calculator
- Keep at least a 20% reserve below the rated force.
- Measure the real sheet thickness before setup.
- Use a wider V-die for high-strength steel and plate.
V die opening and air bending force
Because the die opening sits below the line in the formula, doubling it halves the force. That is the main lever when a press is short of capacity: moving 3 mm steel from a 24 mm to a 32 mm die cuts the force by a quarter. The trade-off is a larger inside radius, which lengthens the flat blank and changes the bend allowance, so recalculate the flat pattern with the bend allowance calculator whenever you change dies.
Sheet metal bending tonnage on short and offset parts
A press brake rated at 100 t over a 3 m bed is designed to spread that load along the bed. Bending a short part in the middle concentrates the force on a small length of tooling and ram, which can damage the punch, the die, or the beam. Machine makers publish a maximum force per meter of tooling and limits for off-center loads. Check both, along with the sheet thickness tolerance; sheet sold by gauge can run thicker than nominal, which the sheet metal gauge calculator helps you confirm.
Press brake tonnage chart: mild steel, air bending
Force per length for mild steel at 450 MPa on a V-die of 8 times the thickness:
| Thickness | V-die (8 x t) | Tonnes per meter | US tons per foot | Inside radius (mm) | Min. flange |
|---|---|---|---|---|---|
| 1 mm | 8 mm | 8.14 | 2.74 | 1.28 | 5.6 mm |
| 1.5 mm | 12 mm | 12.22 | 4.10 | 1.92 | 8.4 mm |
| 2 mm | 16 mm | 16.29 | 5.47 | 2.56 | 11.2 mm |
| 3 mm | 24 mm | 24.43 | 8.21 | 3.84 | 16.8 mm |
| 4 mm | 32 mm | 32.58 | 10.95 | 5.12 | 22.4 mm |
| 5 mm | 40 mm | 40.72 | 13.68 | 6.40 | 28 mm |
| 6 mm | 48 mm | 48.87 | 16.42 | 7.68 | 33.6 mm |
| 8 mm | 64 mm | 65.16 | 21.89 | 10.24 | 44.8 mm |
| 10 mm | 80 mm | 81.45 | 27.37 | 12.80 | 56 mm |
| 12 mm | 96 mm | 97.74 | 32.84 | 15.36 | 67.2 mm |
Sheet metal bending force by material: 3 mm on a 24 mm die
| Material | Tensile strength | Tonnes per meter | Inside radius (mm) |
|---|---|---|---|
| Mild steel S235 / A36 | 450 MPa | 24.43 | 3.84 |
| Structural steel S355 | 550 MPa | 29.86 | 4.08 |
| Stainless steel 304 | 650 MPa | 35.29 | 5.04 |
| Aluminum 5052-H32 | 230 MPa | 12.49 | 3.36 |
| Aluminum 6061-T6 | 310 MPa | 16.83 | 3.60 |
| Brass | 400 MPa | 21.72 | 3.60 |
Press Brake Tonnage Calculator FAQ
How do you calculate press brake tonnage?
Multiply 1.42 by the tensile strength in MPa and the thickness squared, divide by the V-die opening, and multiply by the bend length in meters. 3 mm mild steel on a 24 mm die needs about 24.4 t per meter.
What V-die opening should I use?
About 8 times the thickness for sheet up to 12 mm, and about 10 times for thicker plate. A smaller die raises the force sharply.
How much more force does stainless steel need?
About 1.4 to 1.5 times mild steel for the same thickness and die, because its tensile strength is higher.
Does bottoming need more tonnage than air bending?
Yes. Bottoming needs roughly 5 times and coining roughly 10 times the air bending force.