🗜️ Press Brake Tonnage

Written and maintained by the PhDino author · Last reviewed 21 September 2026 · A documented rule of thumb, pinned by automated tests · how PhDino checks its numbers

Estimating the tonnage a press brake needs to air-bend a given sheet metal thickness.

Air bending — the most common press brake bending method — forms a bend by pressing a punch partway into a V-shaped die opening, without bottoming the material fully into the die. The force required depends on the material's tensile strength, its thickness, and critically the width of the V-die opening used: a narrower die opening concentrates the same bending force over a shorter span, requiring proportionally more tonnage.

Tonnage requirements are conventionally expressed per linear foot of bend length, since a press brake's total capacity is what actually limits how long a bend it can make in one pass at a given thickness — a longer bend simply needs proportionally more total tonnage from the same per-foot requirement.

Key formula

Tonnage per foot = 575 × (tensile strength ÷ 60 ksi) × thickness² ÷ die opening width
Total tonnage = tonnage per foot × (bend length ÷ 12)

Variables

575

the common chart constant for 90° air bending of mild steel at about 60 ksi tensile strength, giving short tons per foot

thickness, die opening

material thickness and V-die width, in the same length unit (inches)

Notes & limitations

• The constant 575 already embeds the strength of ordinary mild steel, so other materials are scaled by their tensile strength relative to 60 ksi: stainless steel needs roughly half again as much tonnage, and soft aluminum roughly half as much. It is an empirical approximation for 90° air bends, not a first-principles derivation, and different sources' constants vary by about ±20%.
• Die opening width is typically chosen as roughly 8 times the material thickness as a starting rule of thumb — too narrow a die for a given thickness both increases required tonnage sharply and risks cracking the material at the bend.