Press Brake Tonnage Calculator
Calculate the estimated bending force required for air bending sheet metal on a press brake. Enter the material strength, sheet thickness, bend length and V-die opening to estimate the required press brake tonnage.
Calculate press brake tonnage
This calculator estimates bending force for V-die air bending.
Enter your values
Preset strengths are general reference values. Use the actual tensile strength for the material grade when available.
Suggested starting V opening based on 8 × material thickness: 24 mm.
Results
Calculation
F = 239.63 kN
How to use the press brake tonnage calculator
Select Metric or US units, choose a material or enter your own tensile strength, then enter the sheet thickness, total bend length and V-die opening.
- Select the material or choose a custom tensile strength.
- Enter the thickness of the sheet or plate.
- Enter the total length of the bend.
- Enter the opening width of the V-die being used.
- Select Calculate to estimate the required air-bending force.
The result is an engineering estimate for air bending. Actual press brake requirements can vary with material grade, tooling geometry, bending method, machine characteristics and operating conditions.
Press brake tonnage formula
The calculator uses the following relationship for estimating the force required for V-die air bending:
- F
- Estimated bending force in kilonewtons (kN)
- Rm
- Material tensile strength in N/mm² or MPa
- L
- Bend length in millimetres
- t
- Material thickness in millimetres
- V
- V-die opening in millimetres
Thickness has a particularly strong effect on the calculated force because material thickness is squared in the formula. Increasing the bend length or tensile strength also increases the required force, while increasing the V-die opening reduces it.
Choosing a V-die opening
V-die opening has a major influence on press brake tonnage. A narrower die opening generally requires more bending force, while a wider opening generally reduces the required force.
As a simple reference, the calculator displays a suggested starting V opening equal to eight times the entered material thickness:
This is a starting reference rather than a tooling specification. The appropriate die opening also depends on material type, required inside radius, bend angle, available tooling and the recommendations of the press brake and tooling manufacturers.
Material tensile strength
Press brake force changes with the tensile strength of the material. Stronger materials generally require greater bending force than lower-strength materials of the same thickness and bend length.
| Material | Reference tensile strength |
|---|---|
| Mild steel | 450 MPa |
| Stainless steel | 600 MPa |
| Aluminium | 310 MPa |
These values are general reference values for calculation purposes. Tensile strength varies substantially between grades, tempers and specifications. Enter the actual tensile strength when reliable material data is available.
Press brake tonnage example
Consider a 1000 mm bend in 3 mm mild steel using a 24 mm V-die opening and a tensile strength of 450 MPa.
Material tensile strength: 450 MPa
Material thickness: 3 mm
Bend length: 1000 mm
V-die opening: 24 mm
This is approximately 24.44 metric tonnes-force or 26.94 US short tons-force.
How material thickness affects tonnage
Material thickness is squared in the bending-force formula, so relatively small increases in thickness can significantly increase the force required.
However, press brake operators also commonly increase the V-die opening when bending thicker material. Because the V opening appears in the denominator of the formula, using a wider die can partly offset the increase in force caused by greater material thickness.
This is why tonnage should always be calculated using the actual thickness and actual tooling configuration rather than estimating from thickness alone.
Air bending, bottoming and coining
This calculator is designed specifically for air bending with a V-die.
Air bending forms the material without forcing it completely into the bottom of the die. Other bending methods, including bottoming and coining, can require substantially different forces and should not be calculated using this page.
If the operation is not conventional V-die air bending, consult the press brake and tooling manufacturer's force charts or engineering guidance for the intended process.
Important press brake considerations
Calculated bending force is only one part of determining whether a press brake setup is appropriate.
- Verify the rated capacity of the press brake.
- Check machine load-distribution and centre-loading limits.
- Confirm the load rating of the punch, die and tooling.
- Use the correct tensile strength for the actual material.
- Confirm the required V opening and inside bend radius.
- Account for the bending method and tooling geometry.
- Follow the machine and tooling manufacturer's instructions.
- Follow applicable workplace procedures and safety rules.
Safety note: This calculator provides an estimated bending force for reference, planning and educational purposes. It does not determine whether a particular machine or tooling setup is safe. Always verify machine capacity, tooling ratings, material specifications and manufacturer requirements before performing a bend.
Frequently asked questions
How do I calculate press brake tonnage?
For V-die air bending, the required force can be estimated from the material tensile strength, bend length, material thickness and V-die opening. Increasing tensile strength, bend length or thickness increases the required bending force.
Does a smaller V-die opening require more tonnage?
Yes. For the same material, thickness and bend length, reducing the V-die opening increases the calculated bending force.
Why does material thickness affect press brake tonnage so much?
Thickness is squared in the air-bending force formula. This means the bending force rises rapidly as the material becomes thicker if the other variables remain unchanged.
Can I use this calculator for stainless steel?
Yes. Select the stainless steel reference value or enter the actual tensile strength for the stainless steel grade being bent. Stainless steel generally requires greater force than mild steel of the same dimensions because of its higher tensile strength.
Can I use the calculator for aluminium?
Yes. Select aluminium or enter the tensile strength for the specific aluminium alloy and temper. Aluminium properties vary considerably between grades.
Does the calculated tonnage mean my press brake can safely make the bend?
No. The calculated force is an estimate of bending force, not a machine or tooling safety rating. Machine capacity, load distribution, tooling ratings and manufacturer requirements must also be checked.
Can this calculator be used for bottoming or coining?
No. This calculator is intended for conventional V-die air bending. Bottoming and coining can require different and substantially higher forces.
Calculation method and references
This calculator uses a commonly published air-bending relationship for estimating press brake force from material tensile strength, bend length, material thickness and V-die opening. Material thickness has a particularly strong effect because it is squared in the calculation.
The calculator also uses eight times the material thickness as a starting reference for V-die opening. This is a widely used guideline for conventional air bending, but the appropriate die opening depends on the material, required bend radius, tooling and the particular bending operation.
For further technical guidance, see Bystronic — How to Calculate Press Brake Tonnage and Bystronic — The Rules of Press Brake Tool Selection .
Calculated tonnage should be treated as an engineering estimate rather than a machine or tooling capacity rating. Actual requirements can vary with material properties, tooling geometry, bending method and machine setup. Always check the current force charts, load limits and operating guidance supplied by the press brake and tooling manufacturer before carrying out a bend.