How to Calculate the V Die Opening for Different Sheet Metal Thicknesses

The Introduction

Are your bends coming out inconsistent? Or are you seeing cracks on the outside radius of your stainless steel parts? 90% of the time, the problem isn’t the machine—it’s the wrong V die opening.
Choosing the correct V-die opening is the single most important decision an operator makes. It affects your bend radius, the tonnage required, and the minimum flange length you can form.

In this guide, we’ll break down the math so you can choose the perfect press brake tooling for every job.

 

1. The Golden Standard: The “Rule of 8”

For 90% of general sheet metal bending (specifically for Mild Steel), we use the industry-standard “Rule of 8”.
The Formula:
V Die Opening = 8 x Material Thickness

Example:
If you are bending a 2mm thick sheet of mild steel:
Calculation: 2mmx8= 16mm

This ratio provides the perfect balance between bending force and angle accuracy. It naturally creates an inside radius equal to about 1/6th of the V-opening, which is ideal for structural strength.

 

2. Adjusting for Materials (Stainless vs. Aluminum)

The “Rule of 8” isn’t one-size-fits-all. Different materials have different tensile strengths, which means you need to adjust your tooling.

A. Stainless Steel (The Harder Material)

Stainless steel has high tensile strength and significant “spring-back.”If you use a V-die that is too small, you risk cracking the material or damaging the tool.

• New Formula: V = 10 x T (or even 12 x T)
• Example (2mm Stainless): 2mmx10=20mm  Use 20mm V Die

 

B. Aluminum (The Softer Material)

Aluminum is soft and can crack if bent too sharply, but it generally requires less force.

Formula: V = 6 x T

Example (2mm Aluminum): 2mmx6=12mm, Use 12mm V die

 

3. The “Danger Zone”: Minimum Flange Length

This is the most common mistake operators make. If your V-die is too wide, your sheet metal will fall into the hole instead of bending.
You must calculate the Minimum Flange Length (b) to ensure the sheet can sit safely across the V-opening.

The Formula:
Minimum Flange = V-Opening x 0.7

Example: If you are using a V20 die: Calculation: 20mmx0.7=14mm Result: Your flange must be at least 14mm long.If your drawing asks for a 10mm flange, a V20 die will not work. You may need to use a smaller die or change the design

 

4. Quick Reference Chart

Here is a quick cheat sheet for selecting the right [press brake tooling](<- Link to Category) based on material thickness.

Material Thickness (T)	Mild Steel (V=8T)	Stainless Steel (V=10T)	Aluminum (V=6T)	Min Flange (Approx)
1.0 mm	V8	V10	V6	5.6 mm (for V8)
2.0 mm	V16	V20	V12	11.2 mm (for V16)
3.0 mm	V24	V32	V18	16.8 mm (for V24)
4.0 mm	V32	V40	V24	22.4 mm (for V32)
6.0 mm	V50	V63	V32	35.0 mm (for V50)

Conclusion: Don’t Guess, Calculate. Using the wrong V die opening leads to inaccurate angles, tool damage, and wasted material. By following these simple formulas, you ensure precise bends and longer tool life. Do you need a specific V-opening that isn’t standard? We manufacture custom press brake dies and punches to fit any unique bending requirement. Contact our engineering team today for a quote! Sources