K-Factor Calculator
K-Factor Calculator — Quickly calculate the sheet metal K-factor, bend allowance, and flat pattern length for accurate fabrication. Use presets, switch units, and export results.
Input Parameters
Diagram
Results
How It’s Calculated
K = t / T
BA = (π × (Ri + K × T) × θ) / 180
BD = A + B – Flat Length
What is K-Factor?
K-factor is a critical parameter in sheet metal bending that represents the ratio of the neutral axis position to the material thickness. During bending, the material on the outside of the bend stretches while the inside compresses. The neutral axis is the theoretical plane within the material that experiences neither tension nor compression.
The K-factor formula is expressed as K = t / T, where t is the distance from the inside bend surface to the neutral axis, and T is the material thickness. This value typically ranges from 0.3 to 0.5, with 0.33 being a common default for mild steel.
How to Use This K-Factor Calculator
Our K-Factor Calculator simplifies the process of determining bend parameters:
- Enter the material thickness (T) and select your preferred units (mm or inches)
- Input the inside bend radius (Ri)
- Specify the bend angle in degrees (0-360)
- Optionally, select a material preset for typical K-factor values
- View instant results for K-factor, neutral axis position, and bend allowance
- Use advanced mode to input flange lengths for flat pattern calculations
K-Factor Formulas and Worked Example
The primary formulas used in sheet metal bending calculations are:
- K-factor: K = t / T
- Bend Allowance (BA): BA = (π × (Ri + K × T) × θ) / 180
- Bend Deduction (BD): BD = 2 × (Ri + T) × tan(θ/2) – BA
- Flat Pattern Length: L = A + B – BD
Example Calculation: For a 2mm thick steel sheet with 3mm inside radius bent at 90°:
- Using K = 0.33 (typical for steel)
- BA = (π × (3 + 0.33 × 2) × 90) / 180 = (π × 3.66 × 90) / 180 = 5.77mm
- If flange lengths A=20mm and B=30mm: Flat Length = 20 + 30 – BD
Common K-Factor Values by Material
| Material | Typical K-Factor | Notes |
|---|---|---|
| Mild Steel | 0.33 | Most common default value |
| Aluminum | 0.43 | Softer material, higher K-factor |
| Stainless Steel | 0.38 | Varies by specific alloy |
| Brass | 0.38 | Moderate springback |
| Copper | 0.41 | Soft, ductile material |
Comparison with Other K-Factor Calculators
| Calculator | Inputs | Outputs | Special Features |
|---|---|---|---|
| CalculatorCave | T, Ri, θ, BA (optional), A/B (optional) | K, BA, BD, Flat Length, Y-factor | Live updates, export, diagram, material presets |
| Competitor A | T, Ri, θ | K, BA | Basic calculation only |
| Competitor B | T, Ri, θ, K | BA | Fixed K-factor input |
Frequently Asked Questions
K-factor is the ratio of the neutral axis position to the material thickness. It represents the location where the material neither stretches nor compresses during bending, and is used to calculate bend allowance and flat pattern length.
K-factor is calculated as K = t/T, where t is the distance from the inside bend surface to the neutral axis, and T is the material thickness. It can also be derived from bend allowance using: K = ((180 × BA)/(π × θ × T)) – (Ri / T).
Typical K-factor values range from 0.3 to 0.5. For mild steel, 0.33 is commonly used. Aluminum typically uses 0.43, while stainless steel may use 0.35-0.45 depending on the specific alloy and bending method.
K-factor is used for sheet metal bending calculations and represents neutral axis position, while Y-factor is related to material properties in plasticity theory. Y-factor = K-factor × π for some calculations, but K-factor is more commonly used in practical sheet metal work.
K-factor is crucial for accurately calculating bend allowance and flat pattern length, which ensures parts fit together properly after bending. Incorrect K-factor values can lead to parts that are too long or too short, causing assembly issues and material waste.
Different materials have different elongation and compression properties, which affect where the neutral axis falls during bending. Softer materials like aluminum typically have higher K-factors (0.4-0.5), while harder materials like stainless steel have lower K-factors (0.35-0.45).