How much tonnage does a press brake need?

Why "how many tons" is the wrong first question

Most first-time buyers fixate on tonnage because it is the one number every listing leads with. A press brake has at least four independent capacities, and tonnage is only one:

• Tonnage — the downward force the ram can apply.
• Bend length — the longest part the bed and ram can actually form.
• Throat depth — the distance from the side frame to the tooling centre, which decides how far a flange can reach into the machine.
• Open height — the daylight between bed and ram at full open, which decides how tall a die stack or how deep a box you can close.

A machine can have plenty of tons and still not bend your part because the bed is too short, the throat too shallow, or the open height will not clear your tooling. Write down the four numbers before you shop by tonnage — tonnage is the last to fix.

What actually drives the tonnage you need

Five inputs decide how hard a bend pushes back; miss one and your estimate is guesswork.

Material strength

Force tracks tensile strength, not the metal's name. Mild steel is the baseline everyone quotes. Stainless is stronger — commonly planned at about 1.5 times the mild-steel force for the same thickness and V-opening. Aluminium is weaker — commonly around half. These are planning ratios, not promises — the exact alloy you run matters more than the label. Pull the tensile strength off the certificate for the alloy you actually bend.

Material thickness

This is the input that bites hardest, because required force rises with the square of thickness. Go from 3 mm to 6 mm and you have not doubled the force, you have roughly quadrupled it. That is why your thickest part, not your typical one, sets the requirement.

V-opening of the bottom die

The V-opening is the width of the notch the punch drives the sheet into. Force falls as the V widens and rises as it narrows. A long-standing rule of thumb for air bending mild steel is a V-opening about 8 times the material thickness — enough for a reasonable radius and a manageable force. Two cautions: a tighter V (say 6x) gives a smaller radius but needs more tonnage and sharper, better-supported tooling; and the 8x figure is a starting point, not a law, so confirm the real opening for your radius and material.

Bend length

Bending force is per unit of length. If a 1-metre bend needs X tonnes, a 2-metre bend of the same section needs about 2X. Your longest bend sets the tonnage, and a machine that bends your short parts fine can stall on a long one in the same gauge. Size for the longest bend you will run, not the average.

Bend method

How you form the angle changes the force as much as the material:

• Air bending — the punch does not bottom out. Lowest force, most flexible, most sensitive to setup. The baseline every other method is measured against.
• Bottoming — the punch forces the sheet to the bottom of the V. Typically needs roughly two to three times the air-bend force in the same tooling.
• Coining / hemming — the material is squeezed past elastic recovery. Can need several times the air-bend force and a much stiffer, better-supported setup.

If you will bottom or hem regularly, size the machine for that method. A tonnage comfortable for air bending can be badly under-rated for bottoming.

A formula you can run yourself

The relationship above collapses into one engineering estimate good enough to buy against, if you treat it as a planning figure:

Use consistent units — thickness, V-opening and bend length in the same length unit, tensile strength in that unit's force per area — and apply the constant from a published air-bend calculator or your tooling maker's tables. What matters for buying is the shape: force grows with strength, thickness-squared and length, and shrinks as the V-opening widens.

The constant here is a planning estimate. Material certificates, tooling geometry and lubrication change the actual force. Confirm every figure against your tooling supplier before you commit to a machine.

What goes wrong when the tonnage is wrong

Too little

• The ram stalls or the hydraulic relief valve trips before the angle forms — you cannot make the part.
• Even when it forms, the angle varies along the length as the frame deflects under overload, so springback is inconsistent.
• Sustained overload stresses the pump, seals and frame, and shortens tooling life.

Too much

• You pay for capacity, shipping weight, floor loading and motor power you never use.
• A machine sized far above your work can be awkward on thin sheet: its ram, stroke and control resolution are tuned for heavier bending, so tight tolerances on light gauge get harder, not easier.
• Bigger daylight and stroke add to height and cycle time.

The goal is not "as big as possible." It is "rated above your worst-case bend, with a margin you can justify."

A press brake tonnage chart you can plan against

The table below turns the formula into numbers you can plan against. It assumes mild steel, air bending, and the common rule of thumb that the V-opening sits at about eight times the material thickness. Treat every figure as a starting point, not a specification — your alloy, tooling condition and bend method all move it.

Multiply the tons-per-foot figure by your bend length in feet for the raw force, then add the usual planning margin. Stainless needs noticeably more than mild steel at the same geometry — roughly 1.5× as a rule of thumb — and bottoming or hemming needs more than air bending. A 40 ton press brake running a 4 ft bend in 1/4" plate (18 × 4 = 72 tons calculated) is not a mismatch you can argue with; it is arithmetic.

How much tonnage for common jobs

Buyers rarely search for a formula — they search for a tonnage. These bands describe what each class typically covers in US job shops, as a rule of thumb:

• Around 30 tons (entry level). Thin sheet up to about 1/8" on short bends — maintenance shops, light brackets, one-off work. A 30 ton press brake is a repair-tool class, not a production machine.
• 40 to 60 tons. The small-shop sweet spot: 1/8" to 3/16" steel over 4 to 6 ft beds, with margin. Most budget press brake buyers in this range are buying the machine they will still be using in ten years.
• 70 to 100 tons. 1/4" steel over 6 to 8 ft — general fabrication, enclosures, ductwork. A 100 ton press brake or 100 ton CNC press brake is where "small shop" machines hand over to general-purpose ones.
• Above 120 tons. 3/8" and up, or long heavy plate — structural and heavy fabrication. Past single-machine bed lengths, look attandem configurations.

The bands overlap because length matters as much as force: a 60 ton machine on a 10 ft bed is doing a different job from a 60 ton machine on a 4 ft bed. Read thesize guide on tonnage versus bed length before you commit to a number.

Working backward from your parts

The method, in order:

1. List your real envelope. Thickest material, longest bend, hardest alloy, smallest V-opening those parts demand.
2. Pick the worst single bend. Usually the thickest, hardest, longest combination — not your most common job.
3. Estimate the force for that bend with the formula above, using the material's actual tensile strength.
4. Add margin. A common planning allowance is roughly 10 to 20 percent above the calculated force, more if your parts push the tooling. Choose a machine rated above that, not wildly above.
5. Check the other three numbers. Confirm bend length, throat depth and open height against the same part. A machine with the right tons can still fail here.

Send us your thickest material, required V-opening and longest bend length and we will size the machine for you against this method. The exact model and rating is a factory specification, not something to guess from a generic table.

Buy the machine for the part, not the tonnage

The mistake is starting from "I need a 100-ton press brake" and then finding a 100-ton machine. Start from the part: its thickness, length, alloy, radius and how you form it. That defines a required force and bed, throat and daylight. A shop bending short, thin aluminium has very different needs from one forming long stainless panels, even if both "need about the same tons" on paper.

This is why small-tonnage, configurable machines matter to many US shops: the work is often short runs of moderate material, and what limits the job is throat depth, open height or a non-standard stroke rather than raw force. If your parts need a modified throat, an enlarged opening or an unusual stroke, that is a geometry conversation, not a tonnage one. See oursmall tonnage range and ourdeep throat options.

If the constraint is capital rather than capacity, the used-versus-new decision is separate — our guide to buying used versus new weighs it honestly.

Questions we get asked

Related: Used vs new press brake ·Small tonnage press brakes ·Deep throat press brakes ·CNC hydraulic press brake range ·Running a press brake on single phase