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Bend Allowance

When a piece of material is formed around the nose bar of a bending brake, the inside of the material (next to the nose bar) becomes compressed, and the outer surface is placed in tension. The actual amount of material used in the bend, or the rounded portions of the material only, is the Bend Allowance. Each end of the bend allowance is bordered by the Bend Tangent Lines.

When we are calculating the amount of material required to form a bend, we should consider each of three parts of a bend. There are two “Flat Leg” sections on either side of the bend, and in between is the “Bend Allowance” portion. The points at which the Bend Allowance meets the Flat Leg section becomes the Bend Tangent Line, or the point at which the bend straightens out to become flat.


A common formula for calculating the amount of material consumed in the bend is:

Bend Allowance = 2 x 3.14 (R + T/2) / 360

This allows us to calculate the amount per degree of bend.

In another form, if our bend is required to be 90°, the formula can be simplified to:

Bend Allowance = 2 x 3.14 (R + T/2) / 4

In both these formulae, R = Radius, and T = Thickness of material.