📐 Bend Allowance Calculator
Calculate material length for sheet metal bending operations
Enter angle between 0° and 180°
Radius of the inner surface of the bend
Typical range: 0.3-0.5 (0.33 is common for mild steel)
How to Use This Calculator
Enter Bend Angle
Input the desired bend angle in degrees (typically 30°, 45°, 60°, 90°, etc.). This is the angle through which the material will be bent.
Enter Inside Radius
Input the inside radius of the bend in millimeters or inches. This is the radius of the inner surface of the bent material, typically determined by the die or tooling used.
Enter K-Factor
Input the K-factor, which represents the location of the neutral axis during bending. Common values: 0.33 for mild steel, 0.4-0.5 for aluminum, 0.3-0.35 for stainless steel.
Enter Material Thickness
Input the thickness of the sheet metal in the same units as the radius. Use consistent units throughout (all metric or all imperial).
Calculate and Use
Click "Calculate Bend Allowance" to get the material length needed for the bend. Add this value to your flat pattern dimensions to get the correct blank size.
Formula
BA = (π/180) × θ × (R + K × T)
where:
- BA = Bend Allowance
- θ = Bend Angle (degrees)
- R = Inside Radius
- K = K-Factor (typically 0.3-0.5)
- T = Material Thickness
Example 1: 90° Bend in Mild Steel
Given: Bend angle = 90°, Inside radius = 2 mm, K-factor = 0.33, Thickness = 1 mm
Calculation: BA = (π/180) × 90 × (2 + 0.33 × 1)
BA = (π/180) × 90 × 2.33
BA = 0.017453 × 90 × 2.33 = 3.662 mm
Example 2: 45° Bend in Aluminum
Given: Bend angle = 45°, Inside radius = 3 mm, K-factor = 0.44, Thickness = 1.5 mm
Calculation: BA = (π/180) × 45 × (3 + 0.44 × 1.5)
BA = (π/180) × 45 × 3.66
BA = 0.017453 × 45 × 3.66 = 2.876 mm
K-Factor Reference Values:
- Mild Steel: 0.32-0.33
- Stainless Steel: 0.30-0.35
- Aluminum: 0.40-0.50
- Copper: 0.35-0.40
- Brass: 0.35-0.40
About Bend Allowance Calculator
The bend allowance calculator determines the amount of material needed to create a bend in sheet metal. When metal is bent, the material on the outside of the bend stretches while the inside compresses. The bend allowance accounts for this deformation and tells you how much extra material length is required for the bend operation.
When to Use This Calculator
- Sheet Metal Fabrication: Calculate blank sizes for bent sheet metal parts
- Metalworking: Determine material requirements for brake press operations
- Manufacturing: Plan production and minimize material waste
- Engineering Design: Design sheet metal components with accurate dimensions
- Quality Control: Verify bend calculations and ensure part accuracy
Why Use Our Calculator?
- ✅ Accurate Calculations: Uses established bend allowance formulas
- ✅ K-Factor Support: Accounts for material-specific neutral axis locations
- ✅ Easy to Use: Simple interface for quick calculations
- ✅ Material Reference: Includes K-factor values for common materials
- ✅ Free Tool: No cost, no registration required
- ✅ Mobile Friendly: Works on all devices
Common Applications
Sheet Metal Fabrication Shops: Fabricators use bend allowance calculations daily to determine the correct blank sizes for parts. This ensures parts fit together correctly and reduces scrap material.
Automotive Manufacturing: Car body panels and chassis components are often made from bent sheet metal. Accurate bend calculations ensure parts meet design specifications and fit properly during assembly.
HVAC Ductwork: Heating, ventilation, and air conditioning systems use many bent sheet metal components. Accurate bend allowances ensure duct sections connect properly and maintain airflow efficiency.
Electronics Enclosures: Computer cases, server racks, and electronic device housings often require precise sheet metal bending. Bend allowance calculations ensure components fit together correctly.
Tips for Best Results
- Always use consistent units (all metric or all imperial) throughout the calculation
- K-factor values are approximate; test with your specific material and tooling for best results
- For air bending, the inside radius is typically 1-3 times the material thickness
- For bottom bending or coining, the radius matches the tooling radius
- Consider springback - the material may spring back slightly after bending, requiring over-bending
- For complex bends with multiple angles, calculate each bend separately and sum the allowances
Frequently Asked Questions
What is bend allowance?
Bend allowance is the amount of material length required to create a bend in sheet metal. It accounts for the stretching on the outside of the bend and compression on the inside, ensuring the final part has the correct dimensions.
What is the K-factor?
The K-factor is a constant that represents the location of the neutral axis (the line that neither stretches nor compresses) during bending. It's typically between 0.3 and 0.5, with 0.33 being common for mild steel. The K-factor depends on material type, thickness, and bending method.
How do I determine the K-factor for my material?
K-factor can be determined experimentally by measuring the actual bend allowance and solving for K, or by consulting material property tables. For most applications, using standard values (0.33 for steel, 0.44 for aluminum) works well. For precision work, conduct test bends and measure the results.
What's the difference between inside radius and outside radius?
Inside radius is the radius of the inner (concave) surface of the bend, while outside radius is the radius of the outer (convex) surface. Inside radius = Outside radius - Material thickness. This calculator uses inside radius, which is typically easier to measure and control.
Can I use this for multiple bends?
Yes, calculate the bend allowance for each bend separately and add them together. Also account for the flat sections between bends. The total blank length = sum of flat sections + sum of all bend allowances.
What if my bend angle is less than 90° or more than 90°?
This calculator works for any bend angle between 0° and 180°. Simply enter the desired angle. Common angles are 30°, 45°, 60°, 90°, 120°, and 135°. The formula automatically accounts for the angle in the calculation.