Engineering calculator
Sheet Metal K-Factor Calculator
Find the K-factor for a single sheet-metal bend from measured bend allowance or test-bend dimensions, ready to validate your flat-pattern settings.
K-factor formula
K = [BA / (θ × π / 180) − R] / T
t = K × T
T is material thickness, R is the finished inside bend radius and BA is the arc length along the neutral axis. The bend angle θ is the rotation from flat in degrees; the inside included angle is 180° − θ.
This is the standard bend-allowance equation rearranged to solve for K. It covers one constant-radius bend, not hems or multi-bend blanks.
Reference: SOLIDWORKS K-factor formulaReference: Autodesk neutral-axis definitionTest-bend dimensions
OSSB = (R + T) × tan(θ / 2)
Outside dimensions: BA = L − A − B + 2 × OSSB
Tangent lengths: BA = L − A − B
L is the original flat blank length. Outside flange dimensions end at the virtual sharp where the outer faces would intersect. Tangent lengths stop at the start of the curved bend. Select the reference that matches your measurements.
Example: T = 2 mm, R = 2 mm, θ = 90° and BA = 4.461 mm give K ≈ 0.4200. The equivalent test bend has outside flanges A = B = 50 mm and a flat length of 96.461 mm.