Bending calculator

Bend Allowance and Bend Deduction Calculator

Use measured Fabworks material and tooling values, or enter generic inputs to calculate bend allowance, outside setback, and bend deduction.

Calculator inputs

Results update as you type. Switch units at any time without changing the physical values.

Set all

Use Fabworks production values

Choose stocked material to load its production bend radius, calibrated K-factor, thickness, and production tool setup.

Only catalog combinations with measured bend calibration are shown.

Stock thickness
0.032 in
Production inside radius
1 mm (0.0394 in)
Calibrated K-factor
0.373
Production tooling
1 mm (0.0394 in) punch nose · 8 mm (0.3150 in) V-die

Fabworks tooling keeps its native metric callout. For air bending, the V-die opening and material response also affect the finished radius, so the preset pairs that radius with the K-factor calibrated for the complete production setup.

Upload a STEP file to Fabworks and we detect the bends, apply the production setup, and calculate the flat pattern for you.

The angle through which the material is bent.

Neutral-axis position as a fraction of thickness.

Results

Bend allowance
0.1024 in
Outside setback
0.1 in
Bend deduction
0.0976 in

Quick answer

How this bend allowance calculator works

Bend allowance is the neutral-axis arc length inside a formed bend. Enter bend angle, inside radius, material thickness, and K-factor to calculate the flat length consumed by the bend and the corresponding bend deduction.

How to use the calculator

  1. 1Choose a Fabworks material preset when the part will be ordered from Fabworks, or use generic inputs for a classroom or outside process.
  2. 2Enter the bend angle (how far the flange turns from flat, 90° for an L-bracket), material thickness, inside radius, and K-factor in the units shown beside each field.
  3. 3Use bend allowance when building a flat pattern from tangent lengths; use bend deduction when starting from outside flange dimensions.
  4. 4Verify a production flat pattern with the actual material lot, grain direction, tooling, and press-brake setup.

Worked example

90-degree steel bend

Inputs
Angle 90°, inside radius 0.040 in, thickness 0.060 in, and K-factor 0.42.
Result
Bend allowance = 0.1024 in; outside setback = 0.1000 in; bend deduction = 0.0976 in.

The allowance follows the neutral axis through the bend. Two outside setbacks minus that allowance gives the bend deduction.

Common questions

What to know before using the result

What is the difference between bend allowance and bend deduction?
Bend allowance is the arc length of the neutral axis. Bend deduction is the amount subtracted from the two outside flange dimensions to obtain the flat length.
Is inside bend radius the same as punch radius?
Not always. Punch radius influences the formed radius, but material, thickness, die opening, process, and springback also matter. Use a measured inside radius or a validated Fabworks preset for production work.
Which K-factor should I use?
Use a measured value from the same material and tooling whenever possible. Generic values are useful for estimates, but they cannot reproduce every press-brake setup.

Formula

BA = θ × (R + K × T)

The bend angle θ is converted to radians. R is inside radius, T is thickness, and K locates the neutral axis through the material thickness.

Engineering references

Assumptions and limits

  • The bend has a constant inside radius and thickness.
  • Fabworks presets use measured production calibration; generic K-factors remain estimates.
  • Bend deduction uses two equal outside setbacks.
Educational estimate
Use this result for learning and early design exploration. Verify safety-critical or production decisions with the governing standard, material data, real tooling, and a qualified engineer.

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