Part definition
Legs are the flat faces measured to the outside edge / apex. Each bend sits between two legs and carries its own angle and inside radius.
Developed flat length
Real parts have more than legs
Holes, notches, tabs, varied bends — Bendline unfolds the whole 3D STEP part to a cut-ready DXF and gives you the exact blank, not an estimate.
How to calculate flat length
The developed (flat) length is the length of sheet you cut before any bending.
Bending removes apparent length at each corner, so you take the sum of the
outside leg lengths and subtract a bend deduction for every bend:
flat = Σ outside legs − Σ BD.
Each bend deduction is BD = 2·OSSB − BA, where the outside setback is
OSSB = tan(θ/2)·(r + t) and the bend allowance is
BA = θ(rad)·(r + K·t). This calculator applies that per bend, using
the shared thickness and K-factor plus each bend's own angle and inside radius, so
parts with mixed bends come out right.
Measuring the legs
Measure each leg to the outside edge — for interior legs, to the theoretical sharp corner (apex) where the two outside faces would meet. That is the convention the bend-deduction method assumes, and it is how most fabrication drawings are dimensioned. If you instead dimension to the bend tangent lines, use the bend-allowance (addition) method covered in the bend allowance calculator.
Worked example
An L-bracket with two 50 mm outside legs, t = 2 mm, r = 2 mm, one 90° bend, K = 0.38: BD = 3.665 mm, so flat = 50 + 50 − 3.665 = 96.335 mm. Add a second identical bend and a third 50 mm leg and the flat becomes 150 − 7.330 = 142.670 mm.