Start with the dimensions you measured.
Bend allowance (BA) is the length along the neutral axis through the curved section. Add it to the straight lengths measured from the tangent points to the free edges.
Bend deduction (BD) relates the same flat blank to the outside mold-line dimensions. Subtract it from the sum of the two outside dimensions, which extend to the virtual sharp.
X and Y end at the virtual sharp, where the extended outside faces meet. Illustrated at 90°; these are not tangent-to-edge straight lengths.
Flat length = straight X + straight Y + BAFlat length = outside X + outside Y − BDFollow one part through both calculations.
Take an illustrative L profile with T = 1 mm, R = 1 mm, K = 0.4, A = 90° and outside dimensions X = Y = 50 mm. K = 0.4 is an example input, not a material recommendation.
| Quantity | Value |
|---|---|
| Outside setback | 2.000000 mm |
| Each straight section | 48.000000 mm |
| Bend allowance | 2.199115 mm |
| Bend deduction | 1.800885 mm |
| Flat length, both paths | 98.199115 mm |
The calculation uses full precision before rounding the displayed numbers. Entering 50 mm as a straight section would describe a different part.
Check the angle convention.
The bend angle A is the amount bent away from the original flat direction. The included angle θ is between the flanges, so A + θ = 180°. At a right angle both are 90°; at other angles, substituting one for the other changes the result.
Try the calculator to switch between conventions while preserving the same physical bend. Our methodology records formulas, references and supported limits.