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Press Brake Tonnage Calculator
Enter the material, sheet thickness, bend length and V-die opening to get the required bending force in tonnes and kN, together with the recommended V-die, the approximate inside radius and the minimum flange length. Free, no sign-up.
Material and sheet
Approximate value; enter the Rm from your material certificate.
Example: 3 mm
Length bent in one stroke; converted to metres in the formula.
Die and machine
Suggested: 8 × 3 = 24 mm → nearest standard V25.
If entered, the machine utilisation is calculated.
How was this calculated?
Bend length
1,000 mm ÷ 1,000 = 1 m
Bending force (air bending, 90°)
1.42 × 420 N/mm² × 3² mm² × 1 m ÷ 25 mm = 214.7 kN
Conversion to tonnes
214.7 kN ÷ 9.81 = 21.89 t
Load per metre
21.89 t ÷ 1 m = 21.89 t/m
Recommended V-die
8 × t up to 3 mm; 8 × 3 mm = 24 mm → nearest standard V25
Approx. inside radius
0.16 × 25 mm = 4 mm
Minimum flange length
0.7 × 25 mm = 17.5 mm
Track cutting and bending jobs in one place
LazerCRM is quoting and job-tracking software for laser cutting and sheet metal job shops; press brake bending jobs are tracked together with the cutting jobs. The interface is currently in Turkish. If you are interested, get in touch with us.
How do you calculate press brake tonnage?
The force a press brake needs depends on the sheet thickness, the bend length, the tensile strength of the material (Rm) and the V-die opening. For air bending at 90°, a widely used approximation is: force (kN) = 1.42 × Rm (N/mm²) × thickness² (mm²) × bend length (m) ÷ V-die opening (mm). Divide the result by 9.81 to convert it to metric tonnes. Example: 3 mm mild steel S235 (Rm ≈ 420 N/mm²), 1,000 mm bend length and a V24 die give 1.42 × 420 × 9 × 1 ÷ 24 ≈ 223.7 kN, i.e. about 22.8 t.
Doubling the thickness quadruples the force. A wider V-die lowers the force but increases the inside radius and the minimum flange length. As a starting point, choose a V-die opening of about 8 × thickness up to 3 mm, 10 × thickness from 3 to 10 mm and 12 × thickness above 10 mm. In mild steel the inside radius is roughly 0.16 × V and the minimum flange length roughly 0.7 × V. Loading a press brake above 80% of its rated capacity is not recommended.
The calculator gives approximate starting values. Rm varies from batch to batch, so use the value from your material certificate. Bottoming and coining need 3–5 times the air bending force. Before bending, check the machine manufacturer's tonnage chart and the load limit of your tooling per metre.
How to use the results
The results are technical estimates. For a binding quote, material price, scrap, labour and your own shop rules also have to be taken into account.
Frequently asked questions
What is the formula for press brake tonnage?
For air bending: force (kN) = 1.42 × Rm × t² × L ÷ V, where Rm is the tensile strength (N/mm²), t the sheet thickness (mm), L the bend length (m) and V the die opening (mm). Divide the kN value by 9.81 to get metric tonnes.
How many tonnes do I need to bend 3 mm steel over 1 metre?
For mild steel S235 (Rm ≈ 420 N/mm²) with a V24 die, about 223.7 kN or 22.8 t; with a V25 die, about 21.9 t. Stainless steel 1.4301 (304, Rm ≈ 600 N/mm²) needs roughly 1.43 times as much force for the same dimensions.
How do I choose the V-die opening?
Start with 8 × thickness for sheets up to 3 mm, 10 × thickness for 3–10 mm and 12 × thickness above 10 mm, then pick the nearest standard V. A narrow V raises the force and the risk of die marks; a wide V increases the inside radius and the minimum flange length.
How are the inside radius and the minimum flange length estimated?
In air bending of mild steel the inside radius is about 0.16 × V and the minimum flange length about 0.7 × V. With a V25 die that gives an inside radius of about 4 mm and a minimum flange of about 17.5 mm. Stainless steel produces a slightly larger radius.
Is the bend safe if the machine tonnage is sufficient?
Not on its own. Avoid loading the machine above 80% of its capacity, and check the load limit of the punch and die per metre, whether a short part concentrates the load on a single tool segment, and whether the load is centred in the machine.
Does bottoming or coining change the tonnage?
Yes. The formula is for air bending. Bottoming and coining require roughly 3–5 times the air bending force, so use the press brake manufacturer's chart for those methods.
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- Sheet metal weight calculatorApproximate sheet weight in kg from length, width, thickness and material density.
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