Calculate required bending tonnage from material type, thickness, bend length, and die opening. Instantly checks if your existing machine is sufficient — covers 10 materials.
Free Tool · Air Bend · Bottom Bending · Coining · Imperial (inches / tons)
Bend Parameters
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PSIpsi
ASTM max tensile — check mill cert or material datasheet.
Rule of thumb: Die opening = 8× material thickness. For T=0.125", recommended V = 1.000"
Lin
Total length of the bend line · 48 in = 4 ft · 96 in = 8 ft
Your Machine (Optional)
MAXtons
Enter 0 to skip machine check. Always allow 20% safety margin.
Results
Enter parameters then hit Calculate
✓
Required Tonnage
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tons total
Tons Per Foot
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tons / linear foot
Inside Bend Radius
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inches (air bend)
Min Flange Length
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inches
Machine Utilization—
Detailed Breakdown
Calculated Output
Required tonnage
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Tonnage per foot
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Recommended capacity (w/ 20%)
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Bend Geometry
Inside bend radius
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Outside bend radius
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Min flange length
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Inputs Used
Material / tensile
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Material factor
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Method factor
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Tooling factor
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Thickness × Die opening
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Bend length
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How Press Brake Tonnage Is Calculated
Press brake tonnage is the force required to bend sheet metal to a specified angle. The industry-standard formula for air bending — the most common method in U.S. fabrication shops — is based on AISI 1035 cold-rolled steel at 60,000 PSI tensile as the baseline material. All other materials are scaled by their tensile strength relative to that baseline. Getting tonnage wrong is the most common cause of tool breakage, machine overload, and inconsistent bend angles.
1 The Core Formula
All dimensions in inches. The constant 575 accounts for the baseline material and unit conversion. Material thickness is squared — doubling thickness quadruples tonnage.
Divide the material's UTS by 60,000 PSI (mild steel baseline). Stainless at 84,000 PSI = factor 1.40. Aluminum at 34,000 PSI = factor 0.57. Higher tensile = more tonnage needed.
Material Factor =
UTS (PSI) ÷ 60,000
Example 304 SS:
84,000 ÷ 60,000 = 1.40
3 Inside Bend Radius
In air bending, the inside radius is determined by the die opening width — NOT the punch radius. Wider die = larger inside radius. Rule: inside radius ≈ 16% of die width.
Start with V = 8× material thickness for mild steel. Go wider (10–12×T) for harder materials to avoid cracking. Narrower die = less radius, more tonnage, sharper bend.
Recommended V-Die:
V = 8 × T (mild steel)
V = 10× T (stainless)
V = 6× T (aluminum)
Pro Tip — Always Add 20% Safety Margin
The calculated tonnage is a theoretical estimate. Real-world factors — friction, material thickness variation, worn tooling, misalignment — all increase actual force. Never run a press brake at more than 80% of rated capacity. If your calculated tonnage is 85 tons, you need a machine rated for at least 102 tons. Overloading a press brake causes permanent ram deflection, damaged tooling, and potentially catastrophic failure.
Material Tensile Strength & Bending Factors
Reference values for U.S. fabrication shops. Material factor = UTS ÷ 60,000 PSI. Always verify against your material test certificate.
Material
UTS (PSI)
Mat. Factor
Rec. V-Die
Springback
Notes
Aluminum 3003-H14 Easy
22,000
0.37
6× T
Low
Soft; very easy to bend; use uncoated tooling
Aluminum 5052-H32 Easy
34,000
0.57
6× T
Low
Good formability; common for enclosures & panels
Aluminum 6061-T6 Medium
58,000
0.97
6–8× T
Medium
Higher strength; crack risk on tight radii — anneal if needed
Mild Steel 1018 / A36 Easy
80,000
1.33
8× T
Medium
Baseline material for all press brake calculations
HSLA Steel A572 Gr.50 Medium
90,000
1.50
8–10× T
Medium-High
Higher yield; needs more springback compensation
AR / Hardox Steel Hard
150,000+
2.50+
10–12× T
High
Abrasion-resistant; requires large radius; crack risk
Stainless 304 / 316 Medium
84,000
1.40
8–10× T
High
Work-hardens — avoid tight radii; high springback
Stainless 17-4PH Hard
120,000
2.00
10× T
Very High
Precipitation-hardened; high springback; specialized tooling
Copper (annealed) Easy
30,000
0.50
6× T
Very Low
Very ductile; minimal springback; polished tooling recommended
Brass 260 (annealed) Easy
50,000
0.83
6–8× T
Low
Free-machining; good formability; uncoated tooling fine
Aluminum 3003-H14Easy
UTS22,000 PSI
Material Factor0.37
Rec. V-Die6× T
SpringbackLow
Aluminum 5052-H32Easy
UTS34,000 PSI
Material Factor0.57
Rec. V-Die6× T
SpringbackLow
Aluminum 6061-T6Medium
UTS58,000 PSI
Material Factor0.97
Rec. V-Die6–8× T
SpringbackMedium
Mild Steel 1018 / A36Easy
UTS80,000 PSI
Material Factor1.33
Rec. V-Die8× T
SpringbackMedium
HSLA A572 Gr.50Medium
UTS90,000 PSI
Material Factor1.50
Rec. V-Die8–10× T
SpringbackMedium-High
Stainless 304 / 316Medium
UTS84,000 PSI
Material Factor1.40
Rec. V-Die8–10× T
SpringbackHigh
Stainless 17-4PHHard
UTS120,000 PSI
Material Factor2.00
Rec. V-Die10× T
SpringbackVery High
AR / Hardox SteelHard
UTS150,000+ PSI
Material Factor2.50+
Rec. V-Die10–12× T
SpringbackHigh
Copper (annealed)Easy
UTS30,000 PSI
Material Factor0.50
Rec. V-Die6× T
SpringbackVery Low
Brass 260 (annealed)Easy
UTS50,000 PSI
Material Factor0.83
Rec. V-Die6–8× T
SpringbackLow
Frequently Asked Questions
This calculator uses the standard U.S. Imperial air bending formula: Tons = [(575 × T²) ÷ V ÷ 12] × L × Material Factor × Method Factor × Tooling Factor — where T is material thickness in inches, V is V-die opening in inches, and L is bend length in inches. The constant 575 is derived from AISI 1035 cold-rolled steel at 60,000 PSI tensile as the baseline. This formula is used by Cincinnati, Bystronic, Accurpress, and most major press brake manufacturers in the U.S.
The standard rule of thumb is V = 8× material thickness for mild steel. For harder materials like stainless steel, use 8–10× T to reduce crack risk. For soft aluminum, 6× T works well. A narrower die opening produces a tighter inside radius and requires more tonnage. A wider die produces a larger radius, reduces tonnage, and reduces springback. Never use a V-die opening smaller than the minimum recommended by your tooling manufacturer — this risks cracking the material and damaging the punch.
Air bending (most common): the punch presses the material into the die but never bottoms out. The inside radius is determined by the die width, not the punch. Requires the least tonnage and is the most flexible method. Bottom bending (bottoming): the punch descends until the material is pressed against the die walls — about 4× the tonnage of air bending. Produces more consistent angles with less springback. Coining: extreme force (10× air bending) stamps the material between punch and die, eliminating springback entirely. Used for tight-tolerance aerospace and medical parts.
In air bending, the inside bend radius is approximately 16% of the V-die opening width — the punch radius is essentially irrelevant to the final part geometry. This means if you want a specific inside radius, you choose your die opening first, then calculate tonnage. A tighter radius (narrower die) requires significantly more tonnage. For most shop work, inside radius ≈ 1× material thickness is the practical minimum before crack risk increases. For stainless and AR steel, minimum radius is typically 1.5–3× material thickness.
Rearranging the formula to solve for thickness: T = √[(Tons × V × 12) ÷ (575 × L × Material Factor)]. For a 90-ton machine (using 80% = 72 tons usable), bending 48" of mild steel (1.33 material factor) with a 1" die: T = √[(72 × 1.0 × 12) ÷ (575 × 4 × 1.33)] = √0.282 = 0.531". So maximum thickness is approximately 1/2" mild steel at 4 ft length. Use this calculator with different thickness values to find your machine's practical limit for each material and length combination.
Minimum flange length is the shortest leg of a bent part that will be properly supported by the die during bending. If the flange is too short, it will slip into the die opening instead of resting on the die shoulders — causing an uncontrolled, inaccurate bend. The minimum flange length is approximately 70% of the V-die opening. For a 1" die: minimum flange ≈ 0.70". This is a hard geometric limit — parts designed with flanges shorter than this minimum require special tooling to form correctly.