K Factor Calculator – Sheet Metal Bending
Calculate the K-factor for sheet metal bending. Enter thickness, inner radius, bend angle, and bend allowance for instant K-factor and neutral axis results.
About This Calculator
The K Factor Calculator helps sheet metal fabricators, engineers, and designers determine the K-factor for bending operations. The K-factor is the ratio of the neutral axis location to the material thickness and is essential for calculating bend allowance, bend deduction, and flat pattern dimensions.
When a metal sheet is bent, the material near the inner surface compresses while the material near the outer surface stretches. The neutral axis is the plane where stress and strain are zero — its position shifts during bending. The K-factor quantifies this shift using the formula K = (180 × BA) / (π × θ × T) − (Ri / T), where BA is the bend allowance, θ is the bend angle, T is the material thickness, and Ri is the inner radius. Once calculated, the neutral axis location is t = K × T.
Accurate K-factor values are critical for precision sheet metal work in industries such as automotive, aerospace, HVAC, and construction. Even small errors in K-factor can lead to incorrect flat pattern lengths, resulting in wasted material and rework. Our calculator provides immediate results with a detailed breakdown and charts to help you visualize the bending parameters.
Regional Notes
Global: The K-factor formula and bending principles are universal in sheet metal engineering. Material thickness and dimensions are entered in millimeters (mm) following international standards. The calculator works for any region, as the K-factor itself is a dimensionless ratio independent of measurement system — though the underlying dimensions must be in consistent units.
Frequently Asked Questions
What is the K-factor in sheet metal bending?
The K-factor is the ratio of the neutral axis location to the material thickness in sheet metal bending. It indicates how far the neutral axis shifts from the inner surface when a metal sheet is bent. A K-factor of 0.33 means the neutral axis lies at one-third of the material thickness from the inner surface.
What is the formula for K-factor?
The K-factor formula is K = (180 × BA) / (π × θ × T) − (Ri / T), where BA is the bend allowance in mm, θ is the bend angle in degrees, T is the material thickness in mm, and Ri is the inner radius in mm.
What is the typical range for K-factor values?
The K-factor typically ranges between 0.30 and 0.50 for most sheet metal materials. A value close to 0.30 indicates the neutral axis is near the inner surface (tight bend), while 0.50 indicates it is at the center of the material thickness (generous bend with large radius).
How does bend radius affect the K-factor?
As the bend radius increases relative to the material thickness, the K-factor tends to increase. A smaller inner radius relative to thickness pushes the neutral axis closer to the inner surface (lower K-factor), while a larger radius allows it to shift toward the center (higher K-factor).
Why is K-factor important in sheet metal fabrication?
K-factor is critical for calculating bend allowance and bend deduction, which determine the flat pattern length needed to produce a bent part. Accurate K-factor values ensure parts are cut to the correct size, reducing material waste and rework in sheet metal fabrication.
How do I find K-factor without knowing bend allowance?
If you do not know the bend allowance, you can estimate the K-factor using the empirical formula K = 0.33 + 0.046 × log10(R/T), where R is the inside radius and T is the material thickness. This estimate typically falls between 0.30 and 0.50 for common materials.
Does material type affect the K-factor?
Yes, material type affects K-factor. Softer materials like aluminum tend to have slightly higher K-factors, while harder materials like stainless steel may have lower K-factors. Material properties like yield strength and tensile strength influence how the neutral axis shifts during bending.