Press Brake Calculator
Pick the right die for each thickness, get the bending force, inside radius and minimum flange, and the flat pattern with bend lines for parts with several bends.
- Free
- No sign-up
- Runs in your browser
Part and tooling
Result
Example materials and dies. Enter your tooling and press under “Your tooling” for a check against your machine.
Flat length
112.37 mm
Die
V12
Recommended · V = 6 × t
Inside radius
1.92 mm
Bending force
21 t
205.9 kN
Force per length
21 t/m
205.9 kN/m
Minimum flange (90°)
8.49 mm
K-factor
0.321
DIN 6935
Profile
OutsideInside
Flat blank with bend lines
Bent dimensions
| Segment | Outside | Inside |
|---|---|---|
| 1 | 30 mm | 28 mm |
| 2 | 60 mm | 56 mm |
| 3 | 30 mm | 28 mm |
Bend lines
| Bend | Angle | Deduction | From left edge |
|---|---|---|---|
| 1 | 90° | 3.82 mm | 28.09 mm |
| 2 | 90° | 3.82 mm | 84.27 mm |
Compare dies
Every die in your library for this material and thickness. Click a row to use it.
| Die | V ÷ t | Radius | Force | Min. flange | Status |
|---|---|---|---|---|---|
| 3 | 1.5 mm | 42 t | 4.24 mm | Narrow | |
| 4 | 1.5 mm | 31.5 t | 5.66 mm | Narrow | |
| 5 | 1.6 mm | 25.2 t | 7.07 mm | Narrow | |
| 6 | 1.92 mm | 21 t | 8.49 mm | Recommended | |
| 8 | 2.56 mm | 15.7 t | 11.31 mm | OK | |
| 10 | 3.2 mm | 12.6 t | 14.14 mm | OK | |
| 12.5 | 4 mm | 10.1 t | 17.68 mm | Wide | |
| 16 | 5.12 mm | 7.9 t | 22.63 mm | Wide | |
| 20 | 6.4 mm | 6.3 t | 28.28 mm | Wide | |
| 25 | 8 mm | 5 t | 35.36 mm | Wide | |
| 31.5 | 10.08 mm | 4 t | 44.55 mm | Wide | |
| 40 | 12.8 mm | 3.1 t | 56.57 mm | Wide | |
| 50 | 16 mm | 2.5 t | 70.71 mm | Wide |
Results are estimates and should be verified for critical engineering or manufacturing applications.
How it works
Choose the material, thickness, bend length and punch radius, then draw the part's profile: the length of each segment and the angle and direction of each bend. The calculator picks the die from your library that best fits the thickness and gives you the force, the inside radius, the minimum flange and the flat length with the position of every bend line.
- Die choice: the recommended die is the one closest to the usual opening for the thickness (about 6 × t under 3 mm, 8 × t up to 9 mm, 10–12 × t for plate) that stays within the die's load and your press capacity. You can pick any other die and compare all of them in the table.
- Inside radius: in air bending the radius is set by the die opening, not the punch, as long as the punch radius is smaller. It's estimated as a fraction of V for each material.
- Flat pattern: from outside or inside dimensions, with the K-factor from the inside radius (DIN 6935) or your own value.
- Your tooling: materials with their tensile strength, your dies (opening, angle and maximum load) and your press capacity and length, saved in your browser.
- Bend sheet (Pro): a one-page PDF with the tooling, the profile, the flat blank and the bend lines, ready for the shop floor.
Everything runs in your browser. For production parts, check the K-factor with a test bend: see the K-factor test bend guide.
Formula
- Force (kN/m) = 1.42 × Rm × t² ÷ V
- Inside radius ≈ V × radius factor (or the punch radius, if larger)
- K = (0.65 + 0.5 × log₁₀(ri ÷ t)) ÷ 2, up to 0.5
- Minimum flange = (V ÷ 2) ÷ cos(angle ÷ 2)
- BA = π ÷ 180 × angle × (ri + K × t) · BD = 2 × tan(angle ÷ 2) × (ri + t) − BA
- Flat length = Σ outside segments − Σ BD
- Rm
- Tensile strength of the material, N/mm²
- t
- Thickness, mm
- V
- Die opening, mm
- ri
- Inside radius, mm
Example
U channel 30 / 60 / 30 mm in 2 mm mild steel, 1 m long (example tooling)
- 1Die: 6 × 2 mm = V12. Inside radius: 0.16 × 12 = 1.92 mm (larger than the 1.5 mm punch)
- 2Force: 1.42 × 435 × 2² ÷ 12 = 205.9 kN/m ≈ 21.0 t for the 1 m bend
- 3K-factor: (0.65 + 0.5 × log₁₀(1.92 ÷ 2)) ÷ 2 = 0.321
- 4BA = π ÷ 2 × (1.92 + 0.321 × 2) = 4.02 mm; BD = 2 × (1.92 + 2) − 4.02 = 3.82 mm
- 5Flat length: 30 + 60 + 30 − 2 × 3.82 = 112.37 mm; bend lines at 28.09 and 84.27 mm
Flat blank of 112.37 mm, bent in a V12 die with about 21 t; minimum flange 8.49 mm.
Assumptions, sources and review
Assumptions and limitations
- Air bending only. Bottoming and coining need several times more force and aren't modeled.
- Force = 1.42 × Rm × t² ÷ V (kN per meter of bend). The formula holds when V is about 8–9 × t and the inside radius is about 0.16 × V; outside that range treat it as a rough guide.
- Inside radius ≈ radius factor × V, or the punch radius when it's larger. Example factors: mild steel 0.16 and stainless 304 0.21 (The Fabricator); corten 0.21, scaled by tensile strength from the 60 KSI baseline. Published values for aluminum range from about 9% to 15% of V; the example uses 0.12.
- Recommended die: the usable die closest to 6 × t under 3 mm, 8 × t under 9 mm, 10 × t under 12 mm and 12 × t above, within 6–12 × t and the die and press limits you enter.
- Minimum flange = (V ÷ 2) ÷ cos(angle ÷ 2), about 0.71 × V at 90°, measured to the mold line. Acute dies and offset tooling need longer flanges.
- K-factor from ri ÷ t with k = 0.65 + 0.5 × log₁₀(ri ÷ t) (based on DIN 6935), K = k ÷ 2, between 0.25 and 0.5. Calibrate it with a test bend for production work.
- A sharp bend is flagged when the punch radius is under 0.63 × t × (Rm ÷ 413.7 MPa).
- Springback, the die shoulder radius and tool deflection are not modeled. The example tensile strengths are the middle of each standard range (S235 360–510 MPa, S355 weathering 470–630 MPa) or a typical value (304: ASTM A240 minimum 515 MPa); use your mill certificate.
Sources
- MachineMFG — Press brake tonnage calculator: P = 1.42 × σb × S² × L ÷ V and its validity
- Bystronic — How to calculate press brake tonnage (material factor = tensile ÷ 60,000 PSI)
- The Fabricator (S. Benson) — Six steps for selecting the right die for press brakes (inside radius as % of V)
- The Fabricator (S. Benson) — How air forming works (sharp bend at 63% of thickness)
- The Fabricator — Press brake bending tips: minimum flange about 70% of the die width
- WILA — V-opening (6–8 × thickness for steel up to about 3 mm)
- Wikipedia (German) — Biegeverkürzung: correction factor k based on DIN 6935
- Arvedi — Structural steels EN 10025-2 (S235 and S355 tensile ranges)
- SSAB — SSAB Weathering 355 (tensile 470–630 MPa, 3–12 mm)
- ATI — ATI 304 stainless steel (ASTM A240: 515 MPa minimum)
The formula and the worked example on this page are checked by automated tests in Oxenly's code.
Last reviewed on October 30, 2026 by Diego Urtado.
Found an error? Report itFrequently asked questions
Which die opening should I use?
A common starting point is a V opening of about 6 times the thickness for sheet under 3 mm, 8 times up to about 9 mm and 10 to 12 times for plate. Narrower dies need more force and leave a tighter radius; wider dies need less force but give a larger radius. Stainless and high-strength steels usually go in wider dies.
How accurate is the tonnage?
It's the usual air bending estimate, valid when the die is about 8 to 9 times the thickness and the radius is the die's natural radius. Real force varies with the actual tensile strength of the batch, so use the value on the mill certificate and keep a safety margin under your press and die limits.
Why doesn't the punch radius set the inside radius?
In air bending the sheet floats over the die and forms a radius that depends on the opening and the material. The punch only sets the radius when its own radius is larger than that natural radius. If the punch radius is much smaller than the thickness, the bend becomes sharp and creases the inside.
Outside or inside dimensions?
Use the ones on your drawing. Outside dimensions go to the outer mold lines (what you measure over the bend with a caliper); inside dimensions go to the inner mold lines. The flat length is the same part either way.
What's free and what's Pro?
All the calculations, the die comparison and your saved tooling are free. The PDF bend sheet for the shop floor is part of Pro.
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