Press Brake Tonnage Calculator — Air Bending Force

Short answerAir-bend tonnage per foot ≈ (575 × t²) ÷ V for 60,000 psi mild steel, where t is thickness and V the die opening (both inches). Scale by the strength ratio for other materials, and use a die V ≈ 8 × t.

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How it's calculated

Air bending force rises with the square of thickness and falls as the die opening widens. The 575 constant assumes 60 ksi mild steel; stainless (~1.5×) and aluminum (~0.5×) scale from it. Multiply the per-foot figure by the bend length, and confirm the die and inside radius suit the part.

Tons/ft ≈ (575 × t²) ÷ V (60 ksi steel) Total tons = Tons/ft × Length(ft) typical die V ≈ 8 × t

Worked example

0.125 in mild steel, V = 1 in.
Tons/ft = 575 × 0.125² ÷ 1 = 9.0 tons/ft.
4 ft → ≈ 36 tons.

Reference tables

Air-bend tons per foot, mild steel (die V = 8×t)

Thickness	V (in)	Tons/ft
0.048 (18 ga)	0.38	3.5
0.075 (14 ga)	0.60	5.4
0.105 (12 ga)	0.84	7.6
0.135 (10 ga)	1.08	9.7
0.250	2.0	18.0

Material strength factor

Material	Factor
Mild steel (60 ksi)	1.0
Stainless	~1.5
Aluminum	~0.5

A number the tables do not give: 10-gauge mild steel over an 8×t die takes roughly 9–10 tons per foot to air bend.

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FAQ

Air bend, bottom or coin?

This is air bending. Bottoming needs ~3–5× the tonnage and coining ~5–8×, so confirm the method before sizing the machine.

How big should the die opening be?

A common rule is V ≈ 8 × thickness for air bending; a wider die lowers tonnage but increases the inside radius.

Does material strength matter?

Strongly — stainless needs about 50% more force and aluminum about half, versus mild steel. Scale the tonnage by the factor.

Why per foot?

Force is proportional to bend length. Compute per foot, then multiply by the total length of the bend.

This page is a reference aid. Always verify against the press-brake and tooling manufacturer charts. Figures shown are for orientation, not a stamped design.

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