Press Brake Tonnage Calculator | Nevatronix Sheet Metal

Press brake tonnage calculator for air bending

Press brake tonnage is the force needed to bend a given material thickness across a given V-die opening. Enter material, thickness, die opening, and bend length below for a live tons-per-foot and total-tonnage estimate, or scroll down for the formula, a mild-steel reference chart, and the rules of thumb behind it.

The formula

This calculator uses the standard published air-bend tonnage rule of thumb, scaled by tensile strength so it works across mild steel, stainless, and aluminum from one formula:

Tons per foot of bend lengthtons/ft = (575 × T² ÷ V) × (UTS ÷ 60,000)

Total tonnagetons = tons/ft × (L ÷ 12)

Where:

T — material thickness, in inches
V — die (V-opening) width, in inches
UTS — the material's ultimate tensile strength, in psi (typical values below)
L — bend length, in inches

The constant 575 and the 60,000 psi baseline are calibrated to mild steel air bending; the UTS ratio scales the estimate for other materials. Typical tensile strength assumed for each material: mild steel ≈ 60,000 psi, stainless (300 series) ≈ 85,000–90,000 psi (this calculator uses 87,500 psi), aluminum 5052-H32 ≈ 30,000–35,000 psi (this calculator uses 32,500 psi). These are typical mill-certification ranges, not a guarantee for your specific heat or lot.

Formula basis: the standard air-bend tonnage rule of thumb published across sheet-metal fabrication trade references, including the Fabricators & Manufacturers Association International (FMA) technical library.

How to read the reference table

Each cell in the table below is tons of force required per linear foot of a 90° air bend in mild steel, at that row's thickness and that column's V-die opening. Multiply by your bend length in feet for total tonnage — or use the calculator above, which does this automatically and also scales for stainless and aluminum. The highlighted cell in each row is the column nearest the 8×T rule of thumb described next.

Why 8×T matters

Die opening is usually chosen relative to material thickness, and 8×T is the standard starting ratio in air-bend practice. Go narrower than roughly 6×T and tonnage climbs sharply — the table below shows how fast the numbers rise toward the tight-die columns — while also raising the risk of galling the material or bottoming the punch before a clean angle forms. Go wider than roughly 10–12×T and tonnage drops, but angle control loosens and the inside radius grows and becomes less repeatable.

As a rule of thumb, the resulting inside bend radius runs about V ⁄ 8 — a 0.750 in die opening produces roughly a 0.094 in inside radius. Treat this as a planning estimate: actual radius depends on material, punch nose radius, and overbend.

Minimum flange (approximation)

A flange shorter than roughly V × 0.7 risks being pulled into the die rather than cleanly bent, or may not clear the die shoulders at all. For a 0.750 in die opening, that puts the approximate minimum flange around 0.525 in. This is a rule-of-thumb floor, not a guarantee — confirm against your actual tooling and back-gauge reach for anything close to it.

Safety note

Every figure on this page is a planning estimate from a published formula, not a substitute for your press brake's or die's rated capacity chart. Never exceed either rating. Actual required tonnage varies with material lot, real tensile strength, friction, bend method, and tooling condition — confirm with your equipment's own chart, and with engineering, before running an unfamiliar setup.

Classic tonnage-per-foot reference — mild steel, air bending

Tons of force required per linear foot of 90° bend, mild steel (≈60,000 psi), computed from the formula above. Bold cells mark the column nearest the 8×T rule of thumb for that row's thickness.

Thickness	Gauge	V = 0.375"	V = 0.500"	V = 0.625"	V = 0.750"	V = 1.000"
0.036"	20 ga	1.99	1.49	1.19	0.99	0.75
0.048"	18 ga	3.53	2.65	2.12	1.77	1.32
0.060"	16 ga	5.52	4.14	3.31	2.76	2.07
0.075"	14 ga	8.63	6.47	5.18	4.31	3.23
0.105"	12 ga	16.91	12.68	10.14	8.45	6.34
0.135"	10 ga	27.95	20.96	16.77	13.97	10.48

Thickness values follow the Manufacturers' Standard Gauge for steel sheet. Values outside roughly 6–12×T for a given row are shown for reference only — see "why 8×T matters" above before picking a die opening far from that band. For stainless or aluminum, use the calculator above.

Frequently asked questions

Why does die opening (V) affect tonnage so much?

Tonnage is inversely proportional to V in the standard air-bend formula, so narrowing the die noticeably increases the force needed for the same thickness. A tighter V also produces a tighter inside radius, which is the main reason shops don't just default to the smallest available die.

What happens if I use a V-opening that's too narrow for my material thickness?

Below roughly 6× material thickness, standard air-bend rules of thumb stop applying — tonnage climbs sharply, the die can gall the material or wear quickly, and the punch can bottom out before reaching a clean angle. Stay near the 8×T rule of thumb unless you have a specific reason, and tooling rated for it, to go tighter.

Is this the exact tonnage my press brake will require?

No — this is a planning estimate from a published rule-of-thumb formula. Actual tonnage varies with material lot, real tensile strength, friction, bend method (air vs. bottom vs. coin), and tooling condition. Always check the result against your machine's and die's rated capacity before running a job.

Why do stainless and aluminum give a different tonnage than mild steel at the same thickness?

Required tonnage scales roughly linearly with the material's tensile strength. Stainless (typically 85,000–90,000 psi) needs meaningfully more force than mild steel (typically 60,000 psi), while soft aluminum alloys like 5052-H32 (typically 30,000–35,000 psi) need less.

What's the difference between air bending, bottom bending, and coining?

This calculator's formula is for air bending — the punch doesn't drive the material fully into the die, and the final angle is set by punch depth. Bottom bending and coining seat the material against the die for a tighter, more repeatable radius, but both require substantially more tonnage than air bending — often several times more.

How do I convert tons per foot to total tonnage for my part?

Multiply tons/ft by the bend length in feet (length in inches ÷ 12). The calculator above does this automatically once you enter a bend length — that total figure is what you compare against your machine's rated tonnage, not the per-foot number.