K-Factor Calculator
Calculate K-factor, neutral axis offset, and neutral axis radius based on bend allowance, bend angle, inside radius, and material thickness. K-Factor Calculator helps fabricators, sheet metal workers, engineers, and construction professionals develop accurate bend layouts and manufacturing specifications.
Highlights
- Calculate sheet metal K-factor from bend allowance, angle, radius, and thickness.
- Determine the neutral axis position for accurate bend layouts.
- Calculate neutral axis offset and radius with reliable results.
- Supports metric and imperial length units, including mm, cm, m, in, and ft.
- Ideal for fabricators, engineers, sheet metal workers, and construction professionals.
Table of Contents
How K-Factor Calculator Works?
The K-factor describes the position of the neutral axis through a sheet during bending. It is defined as the ratio of the neutral-axis offset from the inside bend surface to the material thickness. The calculator uses bend allowance, bend angle, inside bend radius, and material thickness to determine this position.
First, the bend angle is expressed in radians for the calculation. The bend allowance is modeled as the arc length along the neutral axis:
Solving this relationship for the K-factor gives:
Here, BA is the bend allowance, θ is the bend angle in radians, R is the inside bend radius, and t is the material thickness. The neutral-axis offset is then calculated by multiplying the K-factor by the thickness:
The neutral-axis radius is the inside bend radius plus this offset:
The calculator accepts bend allowance, inside bend radius, and material thickness in mm, cm, m, in, or ft. Bend angle can be entered in degrees or radians. The outputs are the K-factor, neutral-axis offset, and neutral-axis radius.
| Quantity | Calculation | Meaning |
|---|---|---|
| K-factor | Neutral-axis position as a fraction of thickness | |
| Neutral-axis offset | Distance from the inside bend surface | |
| Neutral-axis radius | Radius from the bend center to the neutral axis |
For example, using a bend allowance of 10 mm, a 90-degree bend, an inside radius of 3 mm, and a thickness of 2 mm gives a K-factor of approximately 1.683, a neutral-axis offset of approximately 3.366 mm, and a neutral-axis radius of approximately 6.366 mm.
Practical Use Cases
Sheet metal fabricators: Fabricators can use the calculator to estimate the neutral-axis location before creating flat patterns, helping determine the developed length required for brackets, panels, enclosures, and formed profiles.
Sheet metal workers: Workers can apply the K-factor and neutral-axis radius to bend-layout tasks when setting out parts for press-brake forming, manual bending, or prototype production.
Mechanical and manufacturing engineers: Engineers can use the results to establish bend allowances and review whether a proposed inside radius, material thickness, and bend angle are consistent with a part's manufacturing specification.
Construction professionals: Construction teams can use the calculator when planning formed flashing, ductwork, architectural sheet components, and other fabricated metal pieces that require accurate bend development.
Accuracy and Limitations
The calculator is mathematically accurate for the supplied bend-allowance model: it uses K = (BA/θ - R)/t, with the bend angle evaluated in radians. Its practical accuracy depends on the bend allowance being measured or specified correctly for the actual material, tooling, grain direction, and forming method. It does not account for springback, plastic-strain variation, material grade, tooling geometry, minimum bend-radius limits, or bend deduction conventions. Inputs must be positive where required, and the bend allowance, inside radius, and thickness must be expressed consistently; unusual values can produce K-factors outside the commonly expected physical range.
Quick Examples
Example #1: Standard 90-Degree Bend
Calculates the K-factor and neutral axis position for a common sheet metal bend.
Example #2: Thick Steel Panel Bend
Evaluates bend geometry for a thick steel panel using a larger inside radius and material thickness.
Example #3: Metric Fabrication Layout
Determines neutral axis measurements for a metric sheet metal layout with a 120-degree bend.
