Punch Force Calculator
Size the press for a punching job. Enter the hole shape (round, rectangle or obround slot) and size, the material thickness, and the material — get the punch force in tons and pounds, the cut perimeter, the shear area, the stripping force, and the press tonnage to plan for, plus by-thickness and by-hole-size tables and a downloadable PDF.
| Thickness | Shear area | Punch force | Plan for |
|---|---|---|---|
| Enter a hole to compare | |||
| Size | Perimeter | Punch force | Plan for |
|---|---|---|---|
| Enter a hole to compare | |||
How to use the punch force calculator
Four quick steps turn a hole, a thickness and a material into the punch force — in tons and pounds — with the cut perimeter, shear area, stripping force and the press tonnage to plan for, plus by-thickness and by-size tables and a downloadable report.
Pick the hole shape
Round, rectangle or obround slot, and enter its size.
Enter the thickness
The sheet or plate thickness being punched, in inches.
Choose the material
Its ultimate shear strength — steel, stainless, aluminum or copper.
Read results & save a PDF
Get the force, stripping force and press tonnage — then download a report.
The formulas behind the force
Punching shears metal around the hole’s edge, so the force is the cut perimeter times the thickness times the shear strength. The shape sets the perimeter; stripping and press margin follow.
▶ Worked example
Punching a 0.5 in round hole in 0.125 in mild steel (shear strength 50,000 psi).
The cut perimeter is π × 0.5 ≈ 1.571 in, so the shear area is 1.571 × 0.125 ≈ 0.196 in².
Force = 0.196 × 50,000 ≈ 9,818 lb = 4.91 tons
The stripping force is about 0.49 tons (10%), and you should plan a press of at least 4.91 × 1.20 ≈ 5.89 tons.
Punch force quick reference
The cut-perimeter formula for each hole shape, the ultimate shear strength of common materials, and the force to punch a 0.5 in round hole by thickness.
| Shape | Cut perimeter | Dimensions |
|---|---|---|
| Round | π × d | diameter d |
| Rectangle | 2 × (w + h) | width w, height h |
| Obround (slot) | 2 × (L − w) + π × w | length L, slot width w |
A longer perimeter means more metal sheared and more force — perimeter, not hole area, drives the force.
| Material | Ultimate shear (psi) |
|---|---|
| Mild steel | 50,000 |
| Stainless 304 | 85,000 |
| Aluminum 6061 | 30,000 |
| Copper | 25,000 |
Nominal values. Shear strength is roughly 0.6–0.8 of tensile and varies with alloy, temper and hardness.
| Thickness | Shear area (in²) | Punch force (tons) | Plan press (+20%) |
|---|---|---|---|
| 0.0625 in (1/16″) | 0.098 | 2.45 | 2.95 |
| 0.090 in | 0.141 | 3.53 | 4.24 |
| 0.125 in (1/8″) | 0.196 | 4.91 | 5.89 |
| 0.1875 in (3/16″) | 0.295 | 7.36 | 8.84 |
| 0.250 in (1/4″) | 0.393 | 9.82 | 11.78 |
| 0.375 in (3/8″) | 0.589 | 14.73 | 17.67 |
Perimeter π × 0.5 = 1.571 in, mild steel 50,000 psi. Enter your own hole, thickness and material above.
Everything the calculator gives you
One hole and material produce a full force profile, not just a single number.
Punch force reference numbers
Built for anyone punching metal
Fabricators, tooling engineers, and makers all need to know the force a punched hole takes.
Running an ironworker or punch press and needing to know whether a hole is within the machine’s tonnage before setting up the job.
- Check the force against the machine’s rating
- Plan the press tonnage with margin
- Compare round, rectangular and slot punches
Designing dies and selecting presses — the punch load, the stripping force, and the margin to spec the machine and the stripper.
- Work out the shear area and punch load
- Estimate the stripping force for the stripper
- Hand a reviewer a clean PDF of the figures
Using a hand, knockout or hydraulic punch and wondering whether the tool can handle a hole in a given material and thickness.
- See the force a hole will take in tons
- Check it against a punch’s rated capacity
- Try different materials and thicknesses
Get a reliable force estimate
Small habits make a punch force estimate far more trustworthy.
Size the press with margin
Plan for a press rated about 20% above the calculated force, not right at it.
Perimeter drives force
It’s the edge length being sheared, not the hole area. A long slot can beat a big round hole.
Thickness scales directly
Double the thickness and you double the force. It’s a straight multiplier.
Shear angles cut peak force
A ground bevel on the punch or die spreads the cut out, lowering the peak load a press sees.
Match the shear strength
Use the value for your exact alloy and temper — stainless needs far more than aluminum.
Don’t forget stripping
The press also has to pull the punch back out — roughly 10% more load on the return.
Confirm before production
Check against the material certificate and the tooling and press maker before a production run.
Frequently asked questions
Common questions about punch force, cut perimeter, and press tonnage.
Punch force is the force needed to shear a hole through sheet or plate. It is the cut perimeter times the material thickness times the material’s ultimate shear strength: force = perimeter x thickness x shear strength.
The perimeter times the thickness is the shear area — the area of metal being sheared around the edge of the hole — and the shear strength is how hard that metal is to cut. Work in inches and psi, and divide by 2,000 to get short tons.
For example, a 0.5-inch round hole (perimeter about 1.571 inches) in 0.125-inch mild steel (shear strength 50,000 psi) needs about 1.571 times 0.125 times 50,000, which is 9,818 pounds, or about 4.91 tons. This calculator does the math for round, rectangular and obround holes.
The cut perimeter is the distance around the edge of the hole being sheared — the longer it is, the more metal is cut and the more force is needed. The formula depends on the shape.
For a round hole it is pi times the diameter. For a rectangle it is twice the sum of the width and height. For an obround slot — a rectangle with semicircular ends — it is twice the straight length minus the width, plus pi times the slot width.
For example, a 0.5-inch round hole has a perimeter of about 1.571 inches. This calculator switches to the right perimeter formula when you choose the shape, and reports the perimeter it used.
Punching shears metal only around the edge of the hole, not across the whole opening, so the force depends on the perimeter and the thickness — the shear area — not on the area of the hole itself.
That is why a long thin slot can take more force than a round hole of the same opening area: it has a longer perimeter. And why punching many small holes can total more force than one large hole of the same total area.
This calculator works out the cut perimeter for your shape and uses it, with the thickness, to find the shear area and the force — so the shape is accounted for correctly.
Use the ultimate shear strength of your specific material, in psi. Typical values are about 50,000 psi for mild steel, 85,000 for 304 stainless, 30,000 for 6061 aluminum and 25,000 for copper.
Shear strength is roughly 0.6 to 0.8 of a material’s ultimate tensile strength, so if you only have the tensile figure you can estimate the shear from it. The exact value shifts with the alloy, its temper and its hardness.
This calculator offers mild steel, stainless, aluminum and copper, but for a precise result use the shear strength from the material certificate for the exact grade and temper you are punching.
Stripping force is the force needed to pull the punch back out of the material after it has gone through. As the punch pierces, the metal grips it, and the press must overcome that grip on the return stroke.
It is much smaller than the punch force — a common rule of thumb is about 5 to 10 percent of it — but the stripper and the tooling still have to be designed to provide it. This calculator estimates the stripping force at about 10 percent of the punch force.
It matters for the stripper spring or plate design and for the overall load on the press, especially when punching many holes or thick, gripping material.
Size the press above the punch force, with margin. A common rule is to plan for a press rated at least about 20 percent above the calculated punch force, so the machine is not working at its limit and has headroom for tool wear and material variation.
So if a hole needs 4.9 tons to punch, plan for a press of at least about 5.9 tons. Punching several holes at once adds their forces together, unless you stagger or step the punches.
This calculator reports the punch force and a suggested press tonnage with a 20 percent margin, so you can match the job to a machine. Always confirm against the press manufacturer’s rating.
The main lever is the shear area — reduce the perimeter or the thickness and the force drops in proportion. But the most common production trick is a shear angle, grinding a slight bevel on the punch or die so the cut happens progressively rather than all at once.
A shear angle can cut the peak force substantially, because not all of the perimeter is sheared at the same instant. Staggering punches so they hit at different times in a multi-hole die does the same across a strip.
This calculator computes the flat-punch force (no shear angle), which is the conservative, highest-force case. A ground shear angle will need less, but the flat figure is the safe one for sizing.
Punch force comes out in pounds when you multiply the perimeter in inches, the thickness in inches and the shear strength in psi. To convert pounds to US short tons, divide by 2,000, since one short ton is 2,000 pounds.
For example, 9,818 pounds divided by 2,000 is about 4.91 tons. Press capacities are usually rated in tons, so this is the figure you compare with the machine.
This calculator reports the punch force in both tons and pounds, along with the cut perimeter, shear area, stripping force and the press tonnage to plan for.
Disclaimer: US units (inches, pounds, short tons). Punch force = cut perimeter × thickness × ultimate shear strength (tons = lb ÷ 2,000). Shear strength values are nominal and vary with alloy, temper and hardness. Shear-angle (beveled) punches, close tooling pitch, work hardening, punch-to-die clearance, lubrication and press condition all change the real force; the stripping force (~10%) and ~20% press margin are rules of thumb. A planning aid only — confirm with the material certificate and the tooling and press manufacturer before production.