The tonnage you need is set by four variables: material thickness, bend length, material tensile strength and V-die opening. For mild steel air bending, tonnage per foot equals 575 multiplied by thickness squared, divided by the V-die opening, then multiplied by bend length in feet. Most general fabrication shops land between 100 and 200 tons.
This guide gives the formula, a ready-reference tonnage chart, the material adjustments that change the answer, and the sizing mistakes that cost fabricators money. All figures reflect air bending, the method used for the majority of production sheet metal work.
What Is the Press Brake Tonnage Formula?
For mild steel air bending: tons per foot = (575 × T²) ÷ V, where T is material thickness in inches and V is the V-die opening in inches. Multiply by bend length in feet for total required tonnage.
Example: 1/4 inch mild steel, 10 foot bend, 2 inch V-die.
- 575 × 0.250² = 35.9
- 35.9 ÷ 2 = 18 tons per foot
- 18 × 10 = 180 tons required
Standard practice is to select a die opening of roughly 8 times material thickness for mild steel. Narrower openings produce a tighter inside radius but raise tonnage sharply.
How Much Tonnage Do I Need by Thickness and Length?
The table below shows approximate air bending tonnage for mild steel at a die opening of 8 times thickness. Use it as a starting point, then confirm with the formula and your actual tooling.
| Material Thickness | Tons / Foot | 4 ft Bend | 8 ft Bend | 10 ft Bend |
|---|---|---|---|---|
| 16 ga (0.060 in) | 4 | 16 tons | 32 tons | 40 tons |
| 14 ga (0.075 in) | 5 | 20 tons | 40 tons | 50 tons |
| 11 ga (0.120 in) | 9 | 36 tons | 72 tons | 90 tons |
| 3/16 in (0.188 in) | 13 | 52 tons | 104 tons | 130 tons |
| 1/4 in (0.250 in) | 18 | 72 tons | 144 tons | 180 tons |
| 3/8 in (0.375 in) | 27 | 108 tons | 216 tons | 270 tons |
| 1/2 in (0.500 in) | 36 | 144 tons | 288 tons | 360 tons |
Note how quickly the requirement scales. Tonnage rises with the square of thickness, so doubling material thickness roughly quadruples the load.
How Does Material Type Change the Tonnage Required?
Material tensile strength changes the answer directly. Apply a multiplier to the mild steel figure.
| Material | Multiplier | 1/4 in over 8 ft |
|---|---|---|
| Aluminum 5052 / 6061 | 0.50 to 0.65 | 72 to 94 tons |
| Mild steel A36 / CRS | 1.00 | 144 tons |
| HSLA 50 ksi | 1.20 to 1.30 | 173 to 187 tons |
| 304 / 316 stainless | 1.45 to 1.60 | 209 to 230 tons |
| AR400 plate | 2.00 or higher | 288 tons or more |
Practical takeaway: if your shop runs both mild steel and stainless, size the machine on the stainless requirement. Sizing on mild steel and then adding stainless work later is one of the most common reasons shops outgrow a machine early.
Does the Bending Method Change Tonnage?
Yes, and dramatically. Air bending is the tonnage-efficient baseline. Bottom bending requires roughly 3 to 5 times the air bending figure. Coining can require 8 to 10 times.
| Method | Relative Tonnage | When It Is Used |
|---|---|---|
| Air bending | 1x | Most production sheet metal work |
| Bottom bending | 3x to 5x | Tighter angle control, less springback |
| Coining | 8x to 10x | Very tight inside radius, maximum repeatability |
If your part drawings call for coined radii, the required machine is far larger than an air bending calculation suggests.
How Much Tonnage Headroom Should I Build In?
Plan on 20 to 30 percent above your calculated maximum. Headroom absorbs three real-world variables: tensile strength variation between material lots, narrower die openings needed for tighter radii, and future work that is heavier than what you run today. Running a machine at or near its rated capacity as routine practice accelerates wear on the ram, cylinders and frame.
Headroom is not a reason to double the machine. Oversizing raises purchase price, floor space, energy draw and, on long beds, the risk of deflection from short center-loaded parts.
What Tonnage Do Different Shop Types Typically Need?
| Shop Type | Typical Material | Typical Tonnage |
|---|---|---|
| HVAC and ductwork | 26 ga to 16 ga galvanized | 40 to 90 tons |
| Enclosure and cabinet fabrication | 16 ga to 11 ga steel, stainless | 60 to 135 tons |
| General job shop | 16 ga to 1/4 in mixed | 100 to 200 tons |
| Structural and heavy plate | 3/8 in to 3/4 in plate | 250 to 600 tons |
| Trailer, tank and equipment OEM | 1/4 in to 1/2 in, long beds | 200 to 400 tons |
What Else Should Be Sized Alongside Tonnage?
Tonnage alone does not define the machine. Confirm four more specifications before purchase:
- Bed length. Exceed your longest bend by 12 to 24 inches.
- Open height and stroke. Must clear your tallest formed flange with tooling installed.
- Tooling system. European quick-change for high-mix work, American style for heavy long runs.
- Back gauge axes. 2-axis for simple flanging, 4 or 6-axis for complex multi-bend parts.
See our hydraulic press brake buyer’s guide for the full specification walkthrough, and our Baykal press brake tonnage guide for model-by-model capacity from 44 tons to 6,600 tons.
Frequently Asked Questions
What tonnage press brake do I need for 1/4 inch steel?
Roughly 18 tons per foot of bend with a 2 inch V-die. That is about 72 tons at 4 feet, 144 tons at 8 feet and 180 tons at 10 feet in mild steel.
What tonnage do I need for 1/2 inch plate?
Approximately 36 tons per foot in mild steel air bending, so about 288 tons across 8 feet. Heavier alloys push that figure well past 400 tons.
Is a 100 ton press brake enough for a small shop?
For sheet work up to about 3/16 inch across 8 feet, yes. If you expect 1/4 inch plate at length or stainless work, 135 to 175 tons is the safer floor.
Does a larger V-die reduce tonnage?
Yes. Tonnage is inversely proportional to die opening. Widening the die lowers required tonnage but increases the inside bend radius, so the part drawing sets the limit.
Can I exceed the rated tonnage occasionally?
No. Rated capacity is a hard limit. Overloading risks frame deflection, cylinder damage and voided warranty coverage.
How do I confirm the right machine for my parts?
Send your heaviest and longest part specifications to Fab-Line Machinery. Our team runs the calculation and recommends tonnage, bed length and tooling.
Get a Tonnage Recommendation
Fab-Line Machinery supplies hydraulic and electric press brakes, hydraulic shears, plasma cutting systems and fiber laser equipment to fabricators across the United States. Send us your part mix and we will size the machine.