Press Brake Tonnage Calculation, Calculator and Chart
The formula, a free calculator and a reference chart for mild steel, stainless steel and aluminium.
Tonnage is the first number to get right when choosing a press brake. Too little and the machine cannot bend your parts; too much and you have paid for capacity you will never use. Here is how press brake tonnage is calculated, with a calculator and a quick-reference table.
The air bending formula
For air bending, the force needed per metre of bend is approximately:
F (kN/m) = 1.42 × UTS × t² / V
- UTS is the tensile strength of the material in N/mm² (about 450 for common mild steel)
- t is the sheet thickness in mm
- V is the die opening in mm
Divide by 9.81 to convert kN to tonnes, then multiply by the bend length in metres. The 1.42 factor already allows for typical die geometry.
Choosing the V-die opening
The usual starting point is a die opening of about 8 times the thickness for sheet up to 6 mm, and about 10 times for thicker plate. A smaller V gives a tighter radius and shorter minimum flange but needs more force; a larger V reduces force but increases the radius and minimum flange.
Tonnage calculator
Press brake tonnage calculator
This is a planning estimate for air bending. Bottoming needs roughly 2-3 times this force, and coining 5 times or more. Always confirm the final selection with the manufacturer.
Quick-reference table
| Thickness | V-die opening | Mild steel (T/m) | Stainless steel (T/m) | Aluminium, soft (T/m) | Approx. inside radius | Min. flange |
|---|---|---|---|---|---|---|
| 1 mm | 8 mm | 8.1 | 12.2 | 4.1 | 1.3 mm | 6 mm |
| 1.5 mm | 12 mm | 12.2 | 18.3 | 6.1 | 1.9 mm | 8 mm |
| 2 mm | 16 mm | 16.3 | 24.4 | 8.1 | 2.6 mm | 11 mm |
| 2.5 mm | 20 mm | 20.4 | 30.5 | 10.2 | 3.2 mm | 14 mm |
| 3 mm | 24 mm | 24.4 | 36.6 | 12.2 | 3.8 mm | 17 mm |
| 4 mm | 32 mm | 32.6 | 48.9 | 16.3 | 5.1 mm | 22 mm |
| 5 mm | 40 mm | 40.7 | 61.1 | 20.4 | 6.4 mm | 28 mm |
| 6 mm | 48 mm | 48.9 | 73.3 | 24.4 | 7.7 mm | 34 mm |
| 8 mm | 80 mm | 52.1 | 78.2 | 26.1 | 12.8 mm | 56 mm |
| 10 mm | 100 mm | 65.1 | 97.7 | 32.6 | 16.0 mm | 70 mm |
| 12 mm | 120 mm | 78.2 | 117.2 | 39.1 | 19.2 mm | 84 mm |
Values are calculated with the formula above, using the default V-die. Stainless steel is taken as 1.5 times and soft aluminium as 0.5 times mild steel.
Worked example
A fabricator wants to bend 2 mm mild steel panels 2500 mm long. Using a 16 mm V-die, the force is about 16 T per metre, or about 41 T over 2.5 m. With a 20% margin, the target is around 50 T, with a working length above 2500 mm. A 40 T machine would be overloaded, and its 2000 mm length too short. The CNC Press Brake 80T (2500 mm) fits, with headroom for occasional 3 mm work over shorter lengths.
Common mistakes
- Using the full machine tonnage on a short part: concentrated loads can damage tools and the ram. Check the tooling's load rating per metre.
- Forgetting stainless steel needs about 50% more force.
- Choosing a very small V-die to get a tight radius, which can double the required force.
- Sizing for a rare job instead of regular work.
Frequently asked questions
How many tons does it take to bend 3 mm mild steel?
About 24 T per metre with a 24 mm V-die, so roughly 61 T for a 2500 mm bend.
How do I calculate tonnage for stainless steel?
Use the stainless steel tensile strength in the formula, or multiply the mild steel figure by about 1.5.