Press Brake Tonnage Calculator
Estimate press brake force for air bending, bottoming or coining from thickness, V-die opening, bend length and tensile strength, with radius and flange rules.
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About this toolWhat is the Press Brake Tonnage Calculator?
Before a bend goes on the brake, someone has to check that the press and the tooling can take it. Too little capacity stalls the ram; too much load concentrated on a short length can crack a die or bow the bed even when the total is under the press rating. This calculator gives the bending force per foot or metre and in total, so you can check both.
Enter the sheet thickness and the bend length, choose the V-die opening or let the tool pick the usual 8 x T, and select a material or type its tensile strength. Air bending is the default; bottoming and coining apply their much larger multipliers. Alongside the force you get the inside radius an air bend will form in that die, the shortest flange that will still sit across the die, and a table showing how force, radius and minimum flange change across die openings from 6 to 12 x T.
- Air bending, bottoming and coining force
- US tons, metric tonnes and kN, per length and in total
- Material presets by tensile strength or custom UTS
- Inside radius and minimum flange rules for the chosen die
- Die opening comparison table and press capacity check
How to use the Press Brake Tonnage Calculator
- Choose metric or inch units and enter the sheet thickness and the length of the bend.
- Let the tool choose the die opening (8 x T, or 10 x T from 1/2 in up), or switch to “My die” and enter your V opening.
- Pick the material, or choose custom and enter the tensile strength and the radius percentage.
- Select air bending, bottoming or coining, and optionally enter your press capacity.
- Read the total force, the force per length, the expected inside radius and the minimum flange, and compare die openings in the table.
Worked examples
3 mm mild steel, 1 m bend, default die
Input
T 3 mm, V 24 mm (8 x T), 1,000 mm long, 60 ksi steel, air bending
Output
25.27 t (247.8 kN), inside radius about 3.84 mm, minimum flange about 16.8 mm
Doubling the bend length doubles the force. Moving to a 30 mm die cuts it by 20% but opens the radius to about 4.8 mm.
1/4 in A36 plate, 10 ft long
Input
T 0.25 in, V 2 in, 120 in, 65 ksi
Output
19.47 tons/ft, 194.7 US tons total
At the 60 ksi baseline this would be the familiar 18 tons per foot. A 175-ton brake is too small for the full length; a 2.5 in die brings it to about 156 tons.
2 mm 304 stainless, 1.5 m
Input
T 2 mm, V 16 mm, 1,500 mm, 85 ksi stainless
Output
35.79 t (351.0 kN), 23.86 t/m, inside radius about 3.36 mm
Stainless needs about 1.4 times the force of mild steel and springs back more. The radius is a larger share of the die opening.
Background and insight
The working formula in tooling catalogues and press makers’ charts is tons per foot = 575 x T² / V, with T and V in inches, for a 90° air bend in mild steel of 60,000 psi tensile strength (AISI 1035 cold-rolled is the usual baseline). Force rises with the square of thickness, because both the bending moment and the section that resists it scale with T, and falls with the die opening, because a wider die gives the punch more leverage. Other materials are scaled by their tensile strength divided by 60 ksi.
In metric units the same relation is about 1.6 x UTS x T² / V in kN per metre, with UTS in MPa and T and V in millimetres. European and Asian brake makers often publish a version with a constant of 1.42 and a 450 MPa baseline, which gives a few percent less; both are rules of thumb for 90° bends and should be checked against the chart for your press.
Air bending touches the sheet at only three points, so the force is low and the radius is set by the die, roughly 15 to 17% of V in mild steel, 20 to 22% in 304 stainless and about 12% in soft 5052 aluminium (Steve Benson’s 20% rule in The Fabricator). Bottoming presses the sheet into the die and needs around five times the air-bend force; coining drives the punch tip into the material and needs ten times or more, which is why it is rarely used on modern brakes.
Common use cases
Checking a job against the press
Make sure the total force and the force per metre stay inside the press and tooling ratings before setting up.
Choosing a V-die
Balance force against inside radius and minimum flange length when picking the die opening.
Design for manufacture
Check that flange lengths and radii on a drawing can actually be formed on the available tooling.
Quoting thicker work
Find out quickly whether a plate job needs a bigger brake or a subcontractor.
Tips and limitations
- Tooling has its own load limit per foot or metre. A short, heavy bend can exceed it even when the press has spare capacity.
- Bend short parts in the centre of the bed and long heavy parts with the load spread evenly to avoid deflecting the ram and bed.
- Use the actual tensile strength from the mill certificate. High-strength steels can need two or three times the force of mild steel.
- Keep V between about 6 and 12 x T. Narrow dies need high force and can crack the outside of the bend; wide dies give large, less predictable radii.
- A flange shorter than about 0.7 x V falls into the die. Use a narrower die or an acute or offset tool for short flanges.
Frequently asked questions
How do you calculate press brake tonnage?
For air bending, tons per foot = 575 x T² / V with T and V in inches for 60 ksi steel. Multiply by the bend length in feet and by the material tensile strength divided by 60 ksi.
What V-die opening should I use?
A common starting point is 8 x the thickness for sheet up to about 1/2 in (12 mm) and 10 x T above that. Narrower dies give tighter radii at higher force.
What inside radius does air bending produce?
Roughly 16% of the die opening in mild steel, 20 to 22% in 304 stainless and about 12% in soft aluminium. The punch radius only controls it when it is larger than this natural radius.
How much more force does bottoming need than air bending?
About five times as much, and coining around ten times or more. That is why most modern brake work is air bent and angles are corrected by depth rather than force.
What is the minimum flange length on a press brake?
About 0.7 x the V-die opening for a standard 90° V die, so a 24 mm die needs a flange of about 17 mm measured to the outside.
Why do metric press brake formulas give different numbers?
They use different baselines, for example 1.42 x 450 MPa instead of 575 tons per foot at 60 ksi, and some include a die-width correction. The results agree within a few percent; the press maker’s chart for your tooling is the reference.
Is there an in-depth guide to the Press Brake Tonnage Calculator?
Yes. “Press Brake Tonnage, V-Die Width and the Air-Bent Radius” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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