Press Brake Tonnage Calculator
Estimate conventional single-bend air-forming force from thickness, bend length, V-die opening and tensile strength.
Preliminary planning estimate, not a verified production setup. Terms and Conditions
Use inches for t, L and V, and psi for ultimate tensile strength S; output is US short tons.
Enter bending dimensions and material
Required values first; optional ratings and adjustments are below.
Bending force estimate
Calculated demand is separate from rated equipment capacity.
Result details and capacity checks
Show calculation stepsConversions, formula substitution, and capacity interpretation
- Enter valid inputs to view the calculation.
Air-bending geometry
Schematic only; proportions are illustrative. V-opening and material thickness update with the inputs.
V opening: 1 in · Sheet thickness: 0.125 in. Diagram not to scale.
Method, sources, and assumptions
Empirical air-bend force estimate; check the complete load path before production.
Bystronic’s 575-coefficient formula uses a 60,000 psi reference material, single-bend conventional air forming, lengths in inches, and US short tons. The material-strength factor is S / 60,000; this is not a machine or tooling approval.
- Example steel tensile strength is 60,000 psi; replace it with the actual material specification.
- Checks apply only to manufacturer ratings supplied by the user, assuming the rated loading conditions are met.
- Local load distribution, tooling suitability, die clearance, bendability, springback, and flange support are not verified.
Sheet metal bending guide
Understanding Your Press Brake Tonnage Result
The press brake tonnage calculator above estimates the total force required for a conventional single air bend from actual sheet thickness, bend length, V-die opening, and ultimate tensile strength. Use its force-per-length result to assess tooling demand, then compare the estimated load against the applicable machine and component ratings. The result is an empirical forming-force estimate—not approval of a production setup.
For example, a 48-inch bend in 0.125-inch steel with a 1-inch V-opening and an illustrative tensile strength of 60,000 psi requires approximately 35.94 US short tons-force under the stated model. That example does not represent every mild-steel grade or guarantee that the bend geometry is achievable.
- Best for
- Preliminary single-air-bend force estimates
- Main output
- Total forming force in US tons-force, metric tonnes-force, or kN
- Next check
- Actual die geometry and manufacturer machine/tooling ratings
Press Brake Tonnage Formula and Inputs
The calculator uses Bystronic’s empirical air-bending relationship for the specified imperial units, with a tensile-strength adjustment to its 60,000 psi steel reference. The main four inputs are required; machine and tooling ratings are optional comparisons.
Conventional single-air-bend force
Multiply 575 by thickness squared and the bend length; divide by twelve times the die opening; then multiply by actual ultimate tensile strength divided by 60,000 psi. The result is in US short tons-force when lengths are in inches and strength is in psi.
The coefficient belongs to this empirical model and unit convention. For conventional single air bending, both the forming-method and specialized-tooling multipliers are 1.0. See Bystronic’s published calculation.
- \(F\)
- Estimated forming forceTotal modeled force along the bend line.
- \(t\)
- Actual thicknessUse measured or specified stock thickness rather than assuming a universal gauge-to-thickness conversion.
- \(L\)
- Bend lengthLength of the bend line formed simultaneously during the press stroke.
- \(V\)
- V-die openingActual opening between the supporting die shoulders, not merely a proposed rule-of-eight opening.
- \(S\)
- Ultimate tensile strengthUse the actual material grade and condition’s ultimate strength. Do not substitute yield strength into this relationship.
Entering values and switching units
Enter thickness and V-opening in inches or millimeters; bend length in inches, feet, millimeters, or meters; and tensile strength in psi, ksi, or MPa. The calculator converts selected units to one consistent internal calculation basis and updates the result automatically. Its 60,000 psi initial value is illustrative, so replace it with the appropriate stock specification.
Use Result units under Advanced options to display the same physical force in US short tons-force, metric tonnes-force, or kilonewtons. One US short ton-force is approximately 8.89644 kN or 0.907185 metric tonnes-force. Avoid mixing a coefficient from a different empirical metric equation into this particular model.
Worked Press Brake Tonnage Example
Estimate the force for a 48-inch single air bend in 0.125-inch steel using a 1.000-inch V-die. Use an illustrative ultimate tensile strength of 60,000 psi so the material correction is 1.0.
Substitute the values
All dimensions are already in inches and strength is in psi. The strength ratio equals 1; 0.125 squared equals 0.015625.
Estimated total forming force
35.94 US short tons-force
Unrounded result: 35.9375 US tons-force, approximately 319.7 kN. This estimates forming demand; machine and tooling suitability remain separate checks.
Total Force vs. Force per Foot
Total forming force is the load predicted for the complete bend. Force per unit length normalizes that load by the simultaneously loaded bend length, making it useful for comparison with manufacturer tooling ratings.
Total force
Compare this with the machine’s applicable load capacity for the actual bend position, length, and loading arrangement—not nominal tonnage alone.
Line load
Compare the calculated kN/m or US tons-force/ft with each tool or holder’s permitted distributed load, using compatible units and loading assumptions.
Quick sensitivity check
With other model inputs fixed, double the bend length to double total force; double thickness to quadruple force; double the V-opening to halve force.
For the reference example, a 24-inch bend instead of 48 inches gives 17.97 US short tons-force when all other inputs stay unchanged. Its calculated force per foot is still approximately 8.98, although loading is concentrated over a shorter tool segment.
The calculator also reports the dimensionless V-opening-to-thickness ratio and an eight-times-thickness comparison. These are geometry cues, not certification that the selected die is appropriate. A surprising result should prompt a check of stock thickness, strength units, bend length, and the actual die opening before any tooling decision.
Choosing a V-Die Opening and Bend Geometry
Increasing the V-opening reduces force in the stated model, but it also changes how the workpiece is supported and can increase its natural inside radius and minimum flange requirement. Check the part drawing before switching to a wider die to lower tonnage.
Three useful starting relationships
For conventional mild-steel air bending, Bystronic’s tooling-selection guidance describes an initial opening around eight times thickness, an approximate natural inside radius around 16% of the die opening, and a minimum flange reference around 77% of that opening for the discussed tooling configuration.
Approximate mild-steel tooling geometry
Choose an initial V-opening of about eight times actual thickness. For the referenced mild-steel setup, estimate natural inside radius at 0.16 times the opening and the minimum flange at 0.77 times the opening. Confirm actual dimensions from the selected tooling and part drawing.
One bend, four die choices
For 0.125-inch material, a 48-inch bend, and the 60,000 psi illustrative strength, these computed force values show the tradeoff. Radius and flange values are approximate references for the cited mild-steel tooling arrangement—not interactive calculator outputs or guaranteed finished dimensions.
| V-opening (in) | Force (US tons-force) | Approx. inside radius (in) | Approx. min. flange (in) |
|---|---|---|---|
| 0.75 | 47.92 | 0.120 | 0.578 |
| 1.00 | 35.94 | 0.160 | 0.770 |
| 1.25 | 28.75 | 0.200 | 0.963 |
| 1.50 | 23.96 | 0.240 | 1.155 |
A wider die can reduce estimated force while increasing the radius or leaving a short flange inadequately supported. Confirm the tooling geometry, punch radius, desired inside radius, material bendability, and flange dimensions before selecting a final die.
Material Strength and Bendability
The formula adjusts the reference force through the entered ultimate tensile strength; it does not determine whether the actual stock will bend to the required radius without cracking or how much it will spring back. Use material-specific information for these separate questions.
Carbon and stainless steel
Verify the actual steel grade, product condition, thickness, and ultimate tensile strength. A generic “steel” value should not stand in for the specified or certified property of the stock used on the shop floor.
Aluminum alloy and temper
Do not treat 5052-H32 and 6061-T6 as interchangeable aluminum. The alloy and temper affect strength and bendability; verify the selected material’s data and forming recommendations.
High-strength materials
A tensile-strength correction to the standard air-bending equation does not establish an acceptable minimum radius. Use the material producer’s bending guidance and the actual tooling geometry, especially for high-strength sheet and plate.
Rolling direction and springback
The bend orientation relative to rolling direction can affect cracking resistance. Springback depends on material behavior and the forming setup; this force calculator does not predict the finished angle or punch penetration needed to reach it.
For a controlled mathematical comparison, changing only the tensile-strength input from 60,000 psi to 90,000 psi increases the model’s predicted force by 50%. That is not a universal “stainless versus mild steel” multiplier; the actual properties and forming method must be checked.
Machine Capacity and Tooling Load Checks
The calculator’s Advanced options compare the estimated demand with ratings supplied by the user. They do not retrieve or verify ratings for a specific machine or tool. Leave a rating blank when unknown; a missing value means that component remains unverified, not that it has unlimited capacity.
Check load per loaded length
For a uniformly distributed modeled load, divide the total force in kilonewtons by the simultaneously loaded bend length in meters to obtain kN/m. Compare that quantity only with a manufacturer rating expressed for an applicable distributed-load condition.
Here, q is estimated line load in kN/m; the numerator is total force in kN and the denominator is loaded length in meters. For illustration, a tool rated at 1,000 kN/m over a uniformly loaded 0.100 m segment corresponds to 100 kN of permissible total segment load under that rating. A machine capable of more total force cannot override the tool’s lower permitted load.
WILA’s load-capacity guidance explains why the tool, holder, and press brake each require verification. Confirm manufacturer restrictions for tool segments, loading positions, and accessories rather than treating a utilization percentage below 100% as a “safe to bend” verdict.
Air Bending, Bottom Bending, and Coining
The calculator above models a conventional single air bend. The same force estimate cannot be used unchanged to select a press brake for bottom bending, coining, hemming, offset forming, or multiple simultaneous bends.
Air bending
The punch forms the sheet against the die shoulders without fully pressing it into the die bottom. The selected empirical equation applies to the conventional single-bend reference configuration.
Bottom bending
Greater contact with the die can require substantially higher force. Actual demand depends on the tooling, material, and forming sequence rather than on a universal correction that the calculator applies automatically.
Coining
High localized pressure produces additional plastic deformation near the bend. A conventional air-bending estimate does not predict its full production-force requirement.
Specialized or simultaneous bends
Offset and hemming tools, among others, can change the required force. Distinguish several bends formed in one stroke from bends performed separately; obtain the appropriate tool-specific factor or manufacturer guidance.
Bystronic gives indicative factors of 5 or more for bottom bending and 10 or more for coining relative to its air-bending reference. These are broad planning indicators, not verified universal multipliers for actual tooling. The calculator intentionally does not apply them.
Calculation Limitations and Common Errors
A valid numerical force is not necessarily a feasible bend. The simplified empirical calculation does not predict finished angle, springback, material cracking, maximum instantaneous force through the stroke, actual flange support, or every machine and tooling limit.
Wrong sheet thickness or gauge
Gauge number alone is not a material-independent thickness. Verify the actual nominal or measured sheet thickness; because the model squares thickness, even a modest thickness error changes force disproportionately.
Incorrect strength or unit
Use ultimate tensile strength. Enter 60,000 psi, 60 ksi, or their equivalent in MPa—not 60 psi when 60 ksi is intended. Do not substitute yield strength without a different validated method.
Wrong bend length or die
Use the bend length formed simultaneously and the actual selected die opening. Adding lengths of separate strokes or applying a hypothetical opening can distort equipment requirements.
Geometry outside model assumptions
A very small V-opening relative to thickness, an unusual profile, or an unsupported short flange may make the empirical result unsuitable for setup decisions. Follow actual tooling and material recommendations.
As a quick check, increasing only thickness by 10% increases the modeled force by 21%; doubling only the V-opening halves it. If the displayed result moves in the opposite direction, recheck the units and values. A small force estimate is not a substitute for assessing physical feasibility.
Press Brake Tonnage Calculator FAQ
How many tons are needed to bend 1/4-inch steel?
There is no single value without bend length, V-opening, material strength, and method. For an illustrative 60,000 psi material, a 36-inch single air bend at 0.25-inch thickness using a 2-inch opening gives approximately 53.91 US short tons-force. Confirm the actual material and equipment ratings.
Can a 100-ton press brake make a bend estimated at 80 tons?
Not on that comparison alone. The nominal machine rating must apply to the actual loading position and bend length, and every punch, die, holder, and clamp must accommodate the applicable load. The calculator does not approve the setup.
Does a 45-degree bend take half the tonnage of a 90-degree bend?
No. Maximum force is not generally proportional to final bend angle, and the maximum during the forming stroke may occur before the finished angle is reached. Do not apply a simple angle/90 multiplier to the conventional air-bending estimate.
Does the calculator predict the finished inside radius or springback?
No. It reports a bending-force estimate and a V-opening-to-thickness comparison. The radius and flange relationships in this article are separate approximate tooling references; neither they nor the calculator predict exact finished geometry or springback.
Why is the measured machine force different from the estimate?
Check whether actual stock thickness and tensile strength match the inputs, whether the selected die opening is correct, and whether the operation is conventional single air bending. Tooling contact, material condition, forming method, and the empirical model’s limitations can also contribute to differences.