K-Factor Calculator

The K-factor is a dimensionless ratio that describes the position of the neutral axis within the sheet metal thickness during bending. It ranges from 0 to 1, where 0 represents the inner surface and 1 represents the outer surface. A K-factor of 0.5 means the neutral axis sits exactly at the center of the sheet.

The K-factor is calculated using the formula: K = (180° × BA) / (π × θ × T) − (Ri / T), where BA is the bend allowance (flat length), θ is the bend angle in degrees, T is the material thickness, and Ri is the inner bend radius. You can enter these values above and the calculator will compute it automatically.

The K-factor is influenced by several factors: the type of material (e.g., aluminum, steel, copper), the bending method (air bending, bottom bending, or coining), the material's hardness and grain direction, tooling geometry, and the ratio of the inner radius to material thickness. Softer materials and larger radius-to-thickness ratios generally yield higher K-factors.

For soft materials like annealed copper, the K-factor is typically around 0.35. Soft brass and aluminum fall around 0.38–0.41. Semi-hard materials sit near 0.43, while hard steel and cold-rolled steel typically range from 0.45 to 0.50. A K-factor of 0.44 is commonly used as a general-purpose default.

The Y-factor (also called the Yoshida factor) is a coefficient derived from the K-factor using the formula: Y = K × π / 2. It is used in some CAD and CAM systems (particularly older DIN-standard tools) as an alternative representation of the neutral axis position. Both describe the same physical property — just in different mathematical forms.

Bend allowance (BA) is the length of material consumed in forming the bend — the arc length along the neutral axis. It is critical for accurately calculating the flat pattern (blank size) of a sheet metal part. If the bend allowance is incorrect, the finished part will be the wrong size after bending.

The neutral axis is an imaginary line within the sheet metal cross-section that experiences neither tension nor compression during bending. On the inner side of the bend, the material compresses; on the outer side, it stretches. The neutral axis lies somewhere between these zones, and its exact position is defined by the K-factor.

Yes. A K-factor above 0.5 means the neutral axis has shifted toward the outer surface, which can occur with very large bend radii relative to thickness. In practice, most air bending operations produce K-factors between 0.38 and 0.50. Values outside the 0–1 range indicate invalid or inconsistent input measurements.