Sheet metal

Reverse K-Factor Solver

Back-solve a K-factor from a measured bend allowance, bend angle, inside radius, and thickness — typically from a coupon-bend test. One coupon is a starting point, not a production K-factor.

mild steel16 ga0.0598 in1.519 mm

Interactive calculator

Reverse K-Factor Solver

Solved K-factor0.420
Measured bend allowance0.1334 in

Static reference

Common thickness, radius, and angle combinations

Swipe table horizontally for more columns.

GaugeThicknessInside radiusAngleBend allowanceBend deduction
16 ga0.0598 in / 1.519 mm0.0598 in / 1.519 mm45 deg0.0667 in0.0324 in
12 ga0.1046 in / 2.657 mm0.1569 in / 3.985 mm90 deg0.3155 in0.2075 in

Formula used

What this calculator computes

K = ((BA / A_rad) − r) / t
K
Solved K-factor (0 to 1)
BA
Measured bend allowance from the coupon (in or mm)
A_rad
Bend angle in radians (A_rad = A × π / 180) (rad)
r
Inside bend radius of the coupon (in or mm)
t
Material thickness (in or mm)
  • Bend angle A is the angle of rotation through which the sheet is bent (the supplement of the included angle for less-than-180° bends). A flat sheet bent so its flanges meet at 90° corresponds to A = 90°. If your drawing labels the included angle, convert with A = 180° − included angle before entering it.
  • If the solved K is outside 0–1 the input data is inconsistent — re-measure or re-check the radius and angle.

Worked example

One numeric walk-through

Inputs

Measured bend allowance BA
0.1334 in
Bend angle A
90°
Inside radius r
0.0598 in
Thickness t
0.0598 in

Steps

  1. A_rad = 90 × π/180 = 1.5708.
  2. BA / A_rad = 0.1334 / 1.5708 = 0.0849.
  3. (BA / A_rad − r) = 0.0849 − 0.0598 = 0.0251.
  4. K = 0.0251 / 0.0598 ≈ 0.42.

Result

Solved K ≈ 0.42 for this coupon. Repeat across the thickness, radius, grain direction, and tooling range you plan to run before committing K to production.

Common mistakes

Things to check before trusting the number

Related calculators

Move between connected shop calculations

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FAQ

Specific checks for this calculator

What measured value do I need for reverse K-factor?

A measured bend allowance from a coupon, plus the coupon's bend angle, inside radius, and thickness. The calculator returns K consistent with those measurements.

Should I solve K-factor from one test coupon?

Use one coupon as a starting point. Confirm K across the thickness, radius, grain direction, and tooling range you plan to run before relying on it for production.