Use this press brake tonnage calculator to estimate the force required to air bend sheet metal. Enter material thickness, bend length, V-die opening, tensile strength, and safety margin to calculate required tonnage, force in kN, load per foot, estimated natural inside radius, and estimated minimum flange length.
The calculator is designed for practical shop-floor estimating and CAD review. It is not a substitute for your press brake manual, tooling catalog, material certificate, operator training, or a test bend on the actual machine and tooling.
Press Brake Tonnage Calculator
Contents
Estimate air-bending tonnage from material thickness, bend length, V-die opening, tensile strength, and safety margin. The calculator also checks V-opening ratio, estimated inside radius, minimum flange length, load intensity, machine capacity, and tooling rating.
| V-opening | Ratio | Required force | Inside radius | Minimum flange |
|---|
What This Calculator Checks
Press brake tonnage is only one part of a safe bending setup. A job can be below the machine total capacity and still overload the machine or tooling locally if the bend is short and thick. That is why this calculator also reports load intensity in tons per foot, tons per inch, and kN per meter.
| Output | Why it matters |
|---|---|
| Required tons | Estimated air-bending force before safety margin. |
| Required tons with margin | A practical planning value for machine selection. |
| Load per foot | Helps check local machine and tooling limits. |
| V-opening ratio | Shows whether the die opening is narrow, normal, or wide for the material thickness. |
| Estimated inside radius | A rough natural radius estimate for air bending. |
| Estimated minimum flange | Flags short flange risks before setup. |
Formula Used
The calculator uses the common imperial air-bending tonnage formula internally. Metric inputs are converted to inches before the calculation.
Required tons = ((575 x T2) / V / 12) x L x material factor
| Variable | Meaning |
|---|---|
| T | Material thickness in inches |
| V | V-die opening in inches |
| L | Bend length in inches |
| Material factor | Tensile strength in PSI divided by 60,000 |
Example Calculation
The default example uses 3.0 mm mild steel, a 1000 mm bend length, a 24 mm V-opening, and a 20 percent safety margin.
| Input or result | Value |
|---|---|
| Material thickness | 3.0 mm |
| Bend length | 1000 mm |
| V-opening | 24 mm, or 8T |
| Tensile strength | 414 MPa, about 60,000 PSI |
| Required force | About 27.85 US short tons |
| With 20 percent safety margin | About 33.42 US short tons |
| Estimated inside radius | About 3.84 mm |
| Estimated minimum flange | About 16.8 mm |
Choosing the V-Die Opening
A common starting point for air bending is a V-opening around 6 to 8 times material thickness, but the best choice depends on material, tooling, bend radius, marking limits, flange length, and available tonnage. A narrower V-opening increases tonnage quickly. A wider V-opening reduces tonnage, but it also increases the natural inside radius and the minimum flange length.
| V/thickness ratio | General status |
|---|---|
| Less than 5T | Very narrow. Verify tooling stress and tonnage carefully. |
| 5T to 6T | Narrow. Check load rating and marking risk. |
| 6T to 12T | Common air-bending range for many jobs. |
| 12T to 19T | Wide. Lower tonnage, larger radius, longer flange requirement. |
| More than 19T | Outside the normal estimate range. Verify with the tooling supplier. |
Inside Radius and Minimum Flange Estimates
For air bending, the calculator estimates natural inside radius as 16 percent of the V-opening and minimum flange length as 70 percent of the V-opening. These are useful planning estimates, not guaranteed production values. Actual results depend on material, tensile strength, grain direction, bend angle, punch radius, die condition, and setup.
Safety Notes
Do not exceed machine or tooling ratings. Confirm both total tonnage and load intensity before bending. Short, thick parts can overload tooling or a press brake centerline even when the total required tonnage looks acceptable. Bottoming and coining are not included in this calculator and can require much higher force than air bending.
Frequently Asked Questions
What is press brake tonnage?
Press brake tonnage is the force required to bend a part. It is usually discussed as total tons for the bend and load intensity such as tons per foot.
Why does thickness affect tonnage so much?
Thickness is squared in the air-bending formula, so a small increase in thickness can create a large increase in required force.
Why does a wider V-die require less tonnage?
A wider V-opening spreads the bend over a larger opening, so less force is needed. The tradeoff is a larger natural inside radius and a longer minimum flange requirement.
Is this calculator for air bending, bottoming, or coining?
This calculator is for air bending only. Bottoming and coining are more process-specific and can require much higher forces.
Can I use this for stainless steel or aluminum?
Yes, as an estimate. Select a material preset or enter the actual tensile strength from your material certificate for a better calculation.
