What is a press brake tonnage chart?
A tonnage chart gives the bending force needed per metre of bend for a given material thickness and V-die opening. The force rises with the square of the thickness and falls as the die opening widens, so the same material bent over a wider V needs much less tonnage.
Mild steel tonnage chart (tonnes per metre of bend, air bending)
Values are tonnes per metre of bend for mild steel of about 450 MPa tensile strength. Multiply by the bend length in metres to get the total force for one bend. The star marks the opening recommended for that thickness, roughly eight times the material thickness.
| t (mm) | Rec. V (≈8t) | V=4 | V=6 | V=8 | V=10 | V=12 | V=16 | V=20 | V=25 | V=32 | V=40 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 0.5 | 4 | 4.1* | 2.7 | 2.0 | 1.6 | 1.4 | 1.0 | 0.8 | 0.7 | 0.5 | 0.4 |
| 0.8 | 6.4 | 10.4 | 6.9 | 5.2 | 4.2 | 3.5 | 2.6 | 2.1 | 1.7 | 1.3 | 1.0 |
| 1 | 8 | 16.3 | 10.9 | 8.1* | 6.5 | 5.4 | 4.1 | 3.3 | 2.6 | 2.0 | 1.6 |
| 1.5 | 12 | 36.6 | 24.4 | 18.3 | 14.7 | 12.2* | 9.2 | 7.3 | 5.9 | 4.6 | 3.7 |
| 2 | 16 | 65.1 | 43.4 | 32.6 | 26.1 | 21.7 | 16.3* | 13.0 | 10.4 | 8.1 | 6.5 |
| 2.5 | 20 | 101.8 | 67.9 | 50.9 | 40.7 | 33.9 | 25.4 | 20.4* | 16.3 | 12.7 | 10.2 |
| 3 | 24 | 146.6 | 97.7 | 73.3 | 58.6 | 48.9 | 36.6 | 29.3 | 23.4* | 18.3 | 14.7 |
| 4 | 32 | 260.6 | 173.7 | 130.3 | 104.2 | 86.9 | 65.1 | 52.1 | 41.7 | 32.6* | 26.1 |
| 5 | 40 | 407.1 | 271.4 | 203.6 | 162.8 | 135.7 | 101.8 | 81.4 | 65.1 | 50.9 | 40.7* |
| 6 | 48 | 586.2 | 390.8 | 293.1 | 234.5 | 195.4 | 146.6 | 117.2 | 93.8 | 73.3 | 58.6 |
| 8 | 64 | 1,042.2 | 694.8 | 521.1 | 416.9 | 347.4 | 260.6 | 208.4 | 166.8 | 130.3 | 104.2 |
| 10 | 80 | 1,628.4 | 1,085.6 | 814.2 | 651.4 | 542.8 | 407.1 | 325.7 | 260.6 | 203.6 | 162.8 |
| 12 | 96 | 2,345.0 | 1,563.3 | 1,172.5 | 938.0 | 781.7 | 586.2 | 469.0 | 375.2 | 293.1 | 234.5 |
How do I read the tonnage chart?
Find the thickness in the first column, follow the row across to the die opening you intend to use, and read the force per metre. Multiply that figure by the actual bend length in metres.
- Step 1: look up the material thickness, t.
- Step 2: pick the column for your V-die opening.
- Step 3: read tonnes per metre and multiply by the bend length in metres.
- Step 4: add 20–30 % reserve for production, and check the figure against the tooling's own rated load per metre.
- If the material is not mild steel, apply the multiplier in the next section.
What about stainless steel, aluminium and high-strength steel?
The chart is for mild steel. Force is proportional to tensile strength, so multiply by the ratio of the material's tensile strength to 450 MPa: about ×1.45 for stainless and high-strength steel, and about ×0.67 for aluminium.
| Material | Reference tensile strength | Multiplier on mild steel tonnage |
|---|---|---|
| Mild steel | 450 MPa | ×1.00 |
| Stainless steel | 650 MPa | ×1.45 |
| High-strength steel | 650 MPa | ×1.45 |
| Aluminium | 300 MPa | ×0.67 |
Does the tonnage chart apply to bottoming and coining?
No. The chart is for air bending, where the punch does not bottom out in the die. Bottoming raises the force moderately, and coining, where the material is pressed fully into the die, can require three to five times the air bending force.
Air bending is the normal method on a CNC press brake because a small change in punch depth changes the bend angle. Bottoming and coining are used when a fixed angle and a tight radius are needed, at the cost of much higher force and dedicated tooling.
How much reserve should I allow above the calculated tonnage?
Add 20 to 30 percent for normal production. The reserve covers material grade variation, full-length bending, and future jobs. A press brake should not be run continuously above about 80 percent of its rated capacity, and the tooling has its own lower load limit.
Related technical pages
Tonnage calculator
Work out the force for one specific job from thickness, length, material and V opening.
V-die opening selection chart
Choose the die opening and see the resulting inner radius and minimum flange.
Tooling load calculator
Check the force per metre against the tooling's own rated load.
Minimum flange calculator
Find the shortest flange a given die opening can form.
Next step
Send us the material, thickness, bend length and V opening and we will confirm the tonnage and recommend a die.
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