Enter the outside dimensions of a part with up to six bends and get the flat blank length plus the position of every bend line, measured from one edge, ready to mark out or program. Handles mixed bend angles and shows the deduction taken at each bend.
Outside dimensions, the way they appear on a drawing. Segments are the flat faces; each bend sits between two of them.
You need one more dimension than you have bends: a part with three bends has four faces. Leave the angle list short and the last value repeats, so "90" gives every bend 90°. Angles are the included angle you would measure on the finished part.
| Bend | Angle | BD | Bend line from edge |
|---|
| Result | Value |
|---|---|
| Sum of outside dims | |
| Total deduction | |
| Inside radius used | |
| K-factor | |
| Minimum flange for this die |
Guidance only. Errors accumulate across bends — check the last flange on a test part before cutting a batch. Full disclaimer.
One bend only? Bend deduction calculator →
Each bend takes its own deduction out of the blank, so a four-bend part has four chances to be wrong. If your K-factor is out by a few hundredths, one bend hides it and four bends put the last flange visibly out of tolerance. On a part that matters, calibrate the deduction on a single test bend in the same material, thickness and die first — then lay out the full part.
The bend line positions above are cumulative from the first edge, because that is how a backgauge works and how a marked-out blank gets checked. Chaining measurements from one bend to the next stacks every small error into the last flange. Measure from a single datum.
A correct flat pattern still needs a workable order of bends. Each formed flange has to clear the punch, the housings and the backgauge fingers when the next bend goes in — a channel with two inward flanges can be geometrically impossible on standard tooling even though the layout is perfect. Work out the sequence before the blank is cut, and check that every flange the backgauge has to reference is long enough and square.
A flange must reach across the die shoulder or the bend will not form — roughly 0.65 × the die opening plus one thickness. On a multi-bend part it is usually the small end flange that fails this, and the calculator flags it above.
Add the outside dimensions of every flat face, then subtract the bend deduction for each bend. The deductions differ if the angles or radii differ, so calculate each one rather than multiplying a single value by the number of bends.
Each bend line sits at the running total of the previous faces, less the deductions already taken, less the outside setback, plus half the bend allowance — which is the centre of the developed arc. Measure every one from the same edge.
Accumulated deduction error. A K-factor that is slightly wrong is invisible on one bend and obvious after four. Calibrate on a test bend, and check whether the material is actually the thickness on the label.
No — the developed length is the same whatever order you bend it in. But the sequence decides whether the part can physically be made, and whether the backgauge has a usable face to reference.
Please read this before using any figure from this page in production.
Every output here is an indicative calculation produced from the values you enter. Real results vary with springback, grain direction, tooling condition and geometry, friction and lubrication, machine calibration and load distribution, temperature, and batch-to-batch variation in material properties. Actual tensile strength commonly differs from the nominal figures listed. Treat these numbers as a starting point to be proven on a test piece — never as a verified value for a production run, a load calculation, or a safety-critical component.
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