Press Brake Tonnage Calculator

Press Brake Tonnage Calculator

Calculate the required bending force (tonnage) for air bending on a press brake. Select your material, enter thickness, die opening, and bend length to get the tonnage in U.S. tons or metric tonnes. Includes a quick-reference tonnage chart for common gauges.

Press brake tonnage is the bending force required to form sheet metal or plate in a V-die. It depends on the material’s ultimate tensile strength, the thickness of the workpiece, the die opening width, and the bend length. Underestimating tonnage risks stalling the ram or damaging tooling; overestimating means tying up a larger machine than the job requires. The standard air-bending formula gives a reliable approximation for selecting the right press brake and die setup.

≈ 11 gauge

Press Brake Tonnage Chart — Mild Steel (60,000 psi)

Tonnage per foot of bend length for air bending mild steel (UTS = 60,000 psi). For other materials, multiply by the ratio of that material’s UTS to 60,000 psi (e.g., for 304 stainless: multiply by 85,000 / 60,000 = 1.42).

Gauge / Thickness 0.500″ Die 0.750″ Die 1.000″ Die 1.500″ Die 2.000″ Die 3.000″ Die 4.000″ Die

Source: Calculated from Machinery’s Handbook 29th Ed., p. 1352, Eq. 36. Tonnage = (12 × T² × 60,000) / (W × 2,000) tons per foot. Highlighted cells show the recommended die opening (≈ 8×T).

Press Brake Bending Force Formula

Air Bending (V-Die)

F = (L × T² × S) / W

where:
F = bending force [force] — e.g. lbf, N, kN
L = bend length [length] — e.g. in, mm
T = material thickness [length] — e.g. in, mm
S = ultimate tensile strength [force / length²] — e.g. psi, MPa
W = die opening (V-width) [length] — e.g. in, mm

Machinery’s Handbook 29th Ed., p. 1352, Eq. 36

To convert the force to U.S. short tons, divide by 2,000 lbs/ton: P (tons) = F / 2,000. For metric tonnes, divide the force in newtons by 9,806.65 N/tonne.

Bend Angle and Force

For air bending, the required force is independent of the bend angle. The punch depth controls the angle — a shallower stroke produces a larger angle, a deeper stroke produces a tighter angle — but the peak bending force is the same. This is why the MH29 formula does not include an angle variable.

Bottom Bending & Coining Multipliers

The air bending formula gives the baseline force. Bottom bending (bottoming) typically requires 2–5× the air bending tonnage. Coining requires 5–10×. This calculator uses 3× for bottom bending and 7.5× for coining as representative mid-range values. Actual multipliers vary by tooling geometry, material, and angle precision required.

How to Use This Calculator

Select your material from the dropdown (or enter a custom tensile strength), then enter the material thickness, die opening, and bend length. The calculator returns the required tonnage instantly. If you are unsure of the die opening, click “Suggest die opening” to apply the standard 8×T rule. For bends along a sheet metal gauge you are not sure about, check the gauge chart to confirm thickness.

Always verify that the total required tonnage does not exceed your press brake’s rated capacity. For long bends, the tonnage is distributed across the bed — check your machine’s per-foot rating. If you need to calculate the weight of the workpiece for handling considerations, use our metal weight calculator.

Worked Example

Problem: Determine the tonnage required to air-bend a 48″ long piece of 10-gauge (0.1345″) mild steel in a 1″ die opening.

Given: L = 48 in, T = 0.1345 in, S = 60,000 psi, W = 1.000 in

F = (48 × 0.1345² × 60,000) / 1.000 = (48 × 0.01809 × 60,000) / 1.000 = 52,100 lbf

P = 52,100 / 2,000 = 26.1 tons

That’s about 6.5 tons per foot of bend. A 50-ton press brake with a 48″ bed has ample capacity for this job. If the same part were 304 stainless steel (85,000 psi), the tonnage would be 26.1 × (85,000 / 60,000) = 36.9 tons.

Frequently Asked Questions

How do you calculate press brake tonnage?

For air bending, the required tonnage is calculated using the formula P = (L × T² × UTS) / (W × 2,000), where L is bend length in inches, T is material thickness in inches, UTS is ultimate tensile strength in psi, and W is the die opening in inches. The result is in U.S. short tons. This formula is from Machinery’s Handbook 29th Ed., p. 1352, Eq. 36.

What is the tonnage for bending 1/4 inch mild steel?

For 1/4 inch (0.250 in) mild steel (60,000 psi UTS) with a standard 2 inch die opening and a 12 inch bend length, the required air bending tonnage is approximately 11.3 tons per foot. Actual tonnage depends on your specific die opening — a narrower die requires more force, and a wider die requires less.

What is the difference between air bending, bottom bending, and coining?

Air bending presses the material into a V-die without the material contacting the die bottom — the bend angle is controlled by punch depth, requiring the least force. Bottom bending (or bottoming) forces the material to conform to the die angle, requiring roughly 2–5 times the air bending tonnage. Coining stamps the material with extreme force to achieve a precise angle with minimal springback, requiring 5–10 times the air bending tonnage. Most modern press brake work uses air bending for its flexibility and lower tonnage requirements.

How do I choose the right die opening for a press brake?

The standard rule of thumb is to use a die opening (V-width) of 8 times the material thickness for material up to about 1/2 inch thick. For material over 1/2 inch, use 10–12 times the thickness. A narrower die opening produces a tighter inside bend radius but requires significantly more tonnage. A wider die reduces force but increases the minimum achievable bend radius. Always verify that the required tonnage does not exceed your press brake’s rated capacity.

How does material type affect press brake tonnage?

Tonnage is directly proportional to the material’s ultimate tensile strength (UTS). Using mild steel (60,000 psi) as a baseline: aluminum 5052-H32 (33,000 psi) requires roughly 55% of the mild steel tonnage, 304 stainless steel (85,000 psi) requires about 142%, and Inconel 625 (120,000 psi) requires about 200%. Always use the specific alloy’s UTS for accurate results.

Why does the formula use ultimate tensile strength instead of yield strength?

MH29 states that during bending, the material is “stressed above the yield strength but below the ultimate tensile strength” (p. 1346) — the outer fibers do not actually reach UTS. The formula uses UTS for two practical reasons. First, it is an empirical formula fitted to experimental bending data, not derived from beam theory — and UTS was found to correlate most consistently with measured forces across different alloys. Second, the ratio of yield strength to tensile strength varies widely between grades (e.g., A36 steel yields at ~60% of UTS, while 304 stainless yields at ~35%), making yield an unreliable input for a general-purpose formula. The formula’s empirical structure effectively scales UTS down to match real-world bending forces, accounting for work hardening in the bend zone without requiring the user to know their material’s exact yield-to-tensile ratio.

Related Calculators

References

  • Oberg, E. et al. Machinery’s Handbook, 29th Edition, Industrial Press, 2012, p. 1352, Eq. 36: bending force formula F = L × T² × UTS / W.
  • Oberg, E. et al. Machinery’s Handbook, 29th Edition, pp. 1346–1347: die bending methods (air bending, bottoming, coining) and bend radius relationships.

Data last verified: April 2026

Request a Quote

Pi Fabricators is a CNC and fabrication shop in Salem, Oregon. We deliver precision-machined and fabricated parts and assemblies to your specifications.

Request a Quote

This calculator is provided for reference only and is offered “as is” without warranty of any kind. Pi Fabricators LLC is not liable for any damages or losses arising from the use of this tool. Verify all critical calculations independently with a qualified professional.

Spot an error on this page? Let us know at Contact@pifabricators.com