Enter the perimeter of the punch, the thickness of the material, and the shear strength of the material to calculate the punching force.

Punching Force Calculator

Enter any 3 values to calculate the missing variable






Punching Force Formula

Punching force is the shearing load required to drive a punch through a material along the full cutting edge. For flat stock, sheet metal, gaskets, plastics, and similar parts, the required force depends on three things: the total cut perimeter, the material thickness, and the material shear strength.

PF = P \times T \times SS
  • PF = punching force
  • P = total perimeter being cut
  • T = material thickness
  • SS = material shear strength

This relationship is linear, which means doubling the perimeter, doubling the thickness, or doubling the shear strength will double the required punching force.

Rearranged Formula Forms

If your calculator is solving for a different variable, these equivalent forms are useful:

P = \frac{PF}{T \times SS}
T = \frac{PF}{P \times SS}
SS = \frac{PF}{P \times T}

How to Use the Calculator

  1. Enter the total perimeter of the feature being punched.
  2. Enter the material thickness.
  3. Enter the material shear strength.
  4. Calculate the missing value.

The most common input mistake is using area instead of perimeter. Punching force is based on the length of material being sheared, not the size of the hole area.

Perimeter for Common Punch Shapes

If you need help determining the perimeter before using the calculator, use the total cutting edge length for the shape being punched.

Circle

P = \pi D

Rectangle

P = 2(L + W)

Slot / Obround

P = 2(L - D) + \pi D

For multiple holes punched at the same time, add the perimeter of every active cut edge to get the total perimeter.

Unit Consistency

Your units must stay consistent across all inputs:

  • If perimeter and thickness are entered in millimeters, shear strength should be in N/mm², kN/mm², or an equivalent metric stress unit.
  • If perimeter and thickness are entered in inches, shear strength should be in psi or ksi.
  • The output force will follow the force unit implied by the shear strength input.

For example, if thickness is in mm and perimeter is in mm, then the force result follows:

mm \times mm \times \frac{N}{mm^2} = N

Approximate Shear Strength Values

The exact value should come from the specific material grade when possible, but these approximate values are often used for quick estimates:

Material Approx. Shear Strength
Aluminum 0.1724 kN/mm²
Brass 0.2412 kN/mm²
Carbon Steel 0.3447 kN/mm²
Stainless Steel 0.5171 kN/mm²

Example

Suppose a punch has a total perimeter of 40 mm, the material thickness is 3 mm, and the material shear strength is 0.1724 kN/mm².

PF = 40 \times 3 \times 0.1724
PF = 20.688 \text{ kN}

That means the ideal cutting force is 20.688 kN, or 20,688 N.

What Increases Punching Force?

  • Greater perimeter: more cutting edge means more force.
  • Greater thickness: thicker stock requires more shearing load.
  • Stronger material: higher shear strength directly increases required force.
  • Simultaneous hits: punching several features at once combines the required force.

Practical Press Sizing Notes

The calculator gives the theoretical shearing force. Real press selection may require additional capacity for:

  • stripper force
  • tool wear and edge condition
  • die clearance effects
  • part ejection and slug control
  • safety margin for production use

Because of that, the required press capacity is often higher than the pure calculated cutting force.

Common Mistakes

  • Using tensile strength instead of shear strength
  • Mixing inch-based dimensions with metric stress units
  • Forgetting to include the full perimeter of all punched features
  • Using nominal part size when the actual cutting profile is more complex

Frequently Asked Questions

Is punching force the same as press tonnage?
Not exactly. Punching force is the calculated shearing load. Press tonnage is the machine capacity needed to safely deliver that load in real operating conditions.

Does hole area matter directly?
No. The force depends on the cut perimeter and thickness, not the enclosed area.

What if I only know the hole diameter?
Calculate the perimeter first for the hole shape, then use that perimeter in the punching force formula.

Can the calculator be used for non-circular punches?
Yes. Any shape can be used as long as you know the total perimeter being cut.