Looking to improve your sheet metal manufacturing process? Look no further than understanding the concept of bend allowance.

When a sheet of metal is bent, it has three dimensions – two outer dimensions and one thickness dimension.

The difference between the sum of the outer dimensions and the unfolded length is known as the bending allowance.

By accurately determining the unfolded length of different sheet metal bends, you can ensure precision and efficiency in your manufacturing process.

But how do you calculate the bending allowance?

This informative article provides a comprehensive explanation of the formula and factors involved, including material thickness, bending angle, inner bending radius, and the K-factor of the material.

It also includes helpful bend allowance charts for common materials like steel, aluminum, and copper.

Whether you’re a seasoned sheet metal manufacturer or just starting out, understanding bend allowance is key to producing high-quality products.

## What Is Bend Allowance?

The concept of bending allowance is as follows: when a sheet of metal is bent, it has three dimensions – two outer dimensions (L1 and L2) and one thickness dimension (T).

It is important to note that the sum of L1 and L2 is greater than the unfolded length (L), and the difference between the two is known as the bending allowance (K).

Hence, the unfolded length of a bend can be calculated as L = L1 + L2 – K.

**Related reading:**

**Why Is Bend Allowance Important?**

The application of the bending coefficient enables us to conduct a comprehensive examination of the bending properties of sheet metal composed of various materials, subject to diverse bending angles and radii.

This allows us to accurately determine the unfolded length of different sheet metal bends, which is essential in the sheet metal manufacturing process.

## Bend Allowance Calculation Formula

How was the formula for bend allowance created? And how do you calculate bend allowance?

To calculate this bending allowance, you can use the following formula:

**Bending Allowance = A*π/180*(R+K*T)**

- BA – Bend Allowance
- A – bend angle in deg
- R – inside bend radius in m
- K – constant
- T – material thickness in m

This formula considers the diverse geometries and properties of the parts to be formed.

The material thickness (T), bending angle (A), inner bending radius (R), and K-factor of the material to be bent are the most critical factors in this calculation.

As evident from the above formula, calculating the bending allowance is a simple process.

You can determine the bending allowance by substituting the aforementioned values into the formula.

When the bending angle is 90°, the bending allowance formula can be simplified as follows:

*Bending Allowance = π/2(R+K*T)*

Note: The K-factor for most standard materials and thicknesses typically falls between 0 and 0.5.

You can accurately calculate the value of the K-factor using the following K-factor calculator:

To simplify the calculation process, you can also use the bending allowance calculator, which is available by scrolling down.

### Bend Allowance Formula for Aluminum

The bending allowance for an aluminum plate is 1.6 times the material thickness subtracted from the sum of two bending lengths.

The formula for calculating the bending of an aluminum plate is L = L1 + L2 – 1.6T, where T represents the thickness of the aluminum plate, L1 and L2 are the two bending lengths, and 1.6T represents the bending allowance.

This value is an empirical value established during production.

To determine the expanded size of the aluminum plate, subtract 1.6 times the material thickness from the sum of the two bending lengths.

It’s important to note that this formula is only applicable to aluminum plates with a bending opening of 6 times the thickness of the aluminum plate.

## Bend Allowance Calculator

The bending allowance calculator provided below simplifies the process of calculating the bending allowance value.

## Bend Allowance Charts for Steel, Aluminum and Copper

The bending allowance table is a convenient resource that lists the thickness, bending radius, bending angle, bending allowance, or bending deduction values of common materials in a tabular format.

This information is stored in a designated location, making it easy to access and select when needed.

**Further reading:**

The tables below provide bending allowances for iron, aluminum, and copper respectively, for reference. They allow you to determine the required bend allowances for different material thicknesses easily.

### Bending allowance chart for cold rolled steel sheet SPCC (electro-galvanized sheet SECC)

TV | Angle | 0.6 | 0.8 | 1 | 1.2 | 1.5 | 2 | 2.5 | 3 | 3.5 | 4 | 4.5 | 5 | Shortest size |

V4 | 90 | 0.9 | 1.4 | 2.8 | ||||||||||

V4 | 120 | 0.7 | ||||||||||||

V4 | 150 | 0.2 | ||||||||||||

V6 | 90 | 1.5 | 1.7 | 2.15 | 4.5 | |||||||||

V6 | 120 | 0.7 | 0.86 | 1 | ||||||||||

V6 | 150 | 0.2 | 0.3 | 0.4 | ||||||||||

V7 | 90 | 1.6 | 1.8 | 2.1 | 2.4 | 5 | ||||||||

V7 | 120 | 0.8 | 0.9 | 1 | ||||||||||

V7 | 150 | 0.3 | 0.3 | 0.3 | ||||||||||

V8 | 90 | 1.6 | 1.9 | 2.2 | 2.5 | 5.5 | ||||||||

V8 | 30 | 0.3 | 0.34 | 0.4 | 0.5 | |||||||||

V8 | 45 | 0.6 | 0.7 | 0.8 | 1 | |||||||||

V8 | 60 | 1 | 1.1 | 1.3 | 1.5 | |||||||||

V8 | 120 | 0.8 | 0.9 | 1.1 | 1.3 | |||||||||

V8 | 150 | 0.3 | 0.3 | 0.2 | 0.5 | |||||||||

V10 | 90 | 2.7 | 3.2 | 7 | ||||||||||

V10 | 120 | 1.3 | 1.6 | |||||||||||

V10 | 150 | 0.5 | 0.5 | |||||||||||

V12 | 90 | 2.8 | 3.65 | 4.5 | 8.5 | |||||||||

V12 | 30 | 0.5 | 0.6 | 0.7 | ||||||||||

V12 | 45 | 1 | 1.3 | 1.5 | ||||||||||

V12 | 60 | 1.7 | 2 | 2.4 | ||||||||||

V12 | 120 | 1.4 | 1.7 | 2 | ||||||||||

V12 | 150 | 0.5 | 0.6 | 0.7 | ||||||||||

V14 | 90 | 4.3 | 10 | |||||||||||

V14 | 120 | 2.1 | ||||||||||||

V14 | 150 | 0.7 | ||||||||||||

V16 | 90 | 4.5 | 5 | 11 | ||||||||||

V16 | 120 | 2.2 | ||||||||||||

V16 | 150 | 0.8 | ||||||||||||

V18 | 90 | 4.6 | 13 | |||||||||||

V18 | 120 | 2.3 | ||||||||||||

V18 | 150 | 0.8 | ||||||||||||

V20 | 90 | 4.8 | 5.1 | 6.6 | 14 | |||||||||

V20 | 120 | 2.3 | 3.3 | |||||||||||

V20 | 150 | 0.8 | 1.1 | |||||||||||

V25 | 90 | 5.7 | 6.4 | 7 | 17.5 | |||||||||

V25 | 120 | 2.8 | 3.1 | 3.4 | ||||||||||

V25 | 150 | 1 | 1 | 1.2 | ||||||||||

V32 | 90 | 7.5 | 8.2 | 22 | ||||||||||

V32 | 120 | 4 | ||||||||||||

V32 | 150 | 1.4 | ||||||||||||

V40 | 90 | 8.7 | 9.4 | 28 | ||||||||||

V40 | 120 | 4.3 | 4.6 | |||||||||||

V40 | 150 | 1.5 | 1.6 |

### Bending allowance chart for aluminum plate

TV | Angle | 0.6 | 0.8 | 1 | 1.2 | 1.5 | 2 | 2.5 | 3 | 3.5 | 4 | 4.5 | 5 | Shortest size |

V4 | 1.4 | 2.8 | ||||||||||||

V6 | 1.6 | 4.5 | ||||||||||||

V7 | 1.6 | 1.8 | 5 | |||||||||||

V8 | 1.8 | 2.4 | 3.1 | 5.5 | ||||||||||

V10 | 2.4 | 3.2 | 7 | |||||||||||

V12 | 2.4 | 3.2 | 8.5 | |||||||||||

V14 | 3.2 | 10 | ||||||||||||

V16 | 3.2 | 4 | 4.8 | 11 | ||||||||||

V18 | 4.8 | 13 | ||||||||||||

V20 | 4.8 | 14 | ||||||||||||

V25 | 4.8 | 5.4 | 6 | 17.5 | ||||||||||

V32 | 6.3 | 6.9 | 22 |

### Bending allowance chart for copper plate

Angle | 0.6 | 0.8 | 1 | 1.2 | 1.5 | 2 | 2.5 | 3 | 3.5 | 4 | 4.5 | 5 | Shortest size |

90 | 3.6 | 5.2 | 6.8 | 8.4 | 28 | ||||||||

120 | |||||||||||||

150 |

### Amada bending allowance chart

MATERIAL | SPCC | SUS | Al （LY12） | SECC | ||||
---|---|---|---|---|---|---|---|---|

T | ΔT | ΔK | ΔT | ΔK | ΔT | ΔK | ΔT | ΔK |

T=0.6 | 1.25 | 1.26 | ||||||

T=0.8 | 0.18 | 1.42 | 0.15 | 1.45 | 0.09 | 1.51 | ||

T=1.0 | 0.25 | 1.75 | 0.20 | 1.80 | 0.30 | 1.70 | 0.38 | 1.62 |

T=1.2 | 0.45 | 1.95 | 0.25 | 2.15 | 0.50 | 1.90 | 0.43 | 1.97 |

T=1.4 | 0.64 | 2.16 | ||||||

T=1.5 | 0.64 | 2.36 | 0.50 | 2.50 | 0.70 | 2.30 | ||

T=1.6 | 0.69 | 2.51 | ||||||

T=1.8 | 0.65 | 3.00 | ||||||

T=1.9 | 0.60 | 3.20 | ||||||

T=2.0 | 0.65 | 3.35 | 0.50 | 3.50 | 0.97 | 3.03 | 0.81 | 3.19 |

T=2.5 | 0.80 | 4.20 | 0.85 | 4.15 | 1.38 | 3.62 | ||

T=3.0 | 1.00 | 5.00 | 5.20 | 1.40 | 4.60 | |||

T=3.2 | 1.29 | 5.11 | ||||||

T=4.0 | 1.20 | 6.80 | 1.00 | 7.00 | ||||

T=5.0 | 2.20 | 7.80 | 2.20 | 7.80 | ||||

T=6.0 | 2.20 | 9.80 |

**Note:**

- The V12 coefficient for 2mm C profile is 3.65 and that for other 2mm plates is 3.5). The edge folding bend allowance for 2mm plate is 1.4;
- The bend allowance for 6mm copper plate is 10.3;
- The bend allowance for 8mm copper plate is12.5;
- The bend allowance for 10mm copper plate is 15;
- The bend allowance for 12mm copper plate is 17;
- The bend allowance for 3.0 stainless steel with V25 die is 6;
- The bend allowance for 3.0 stainless steel with V20 die is 5.5;
- (The copper bars exceeding 6mm all use the bending allowance of V40 lower die)

## FAQs

**1. What is the bend allowance formula, and why is it important in sheet metal fabrication?**

A: The bend allowance formula is a mathematical equation used to calculate the length of the neutral axis between the bend lines in sheet metal fabrication. It is essential for determining the accurate flat pattern size required for bending, ensuring that the final bent part meets the desired dimensions and specifications.

**2. What factors are considered in the bend allowance formula?**

A: The bend allowance formula takes into account the material thickness, bend radius, bend angle, and K-factor (a ratio representing the location of the neutral axis relative to the material thickness). These factors help accurately calculate the length of material needed to accommodate the bend.

**3. How does the K-factor affect the bend allowance formula?**

A: The K-factor is a crucial parameter in the bend allowance formula, as it represents the ratio of the neutral axis to the material thickness. It helps determine the amount of stretching or compression that occurs during the bending process, which directly impacts the bend allowance calculation.

**4. Can the bend allowance formula be applied to all types of sheet metal materials?**

A: The bend allowance formula can be applied to various sheet metal materials, such as aluminum, steel, and stainless steel. However, it is essential to consider the specific material properties, such as the K-factor and material thickness, to ensure accurate bend allowance calculations.

**5. How can I determine the K-factor for a specific material and bending operation?**

A: The K-factor can be determined through empirical testing, by consulting material-specific guidelines, or by using software tools designed for sheet metal fabrication. It is essential to use the correct K-factor for the specific material and bending operation to ensure accurate bend allowance calculations.

**6. What is the difference between bend allowance and bend deduction?**

A: Bend allowance is the length of the neutral axis between the bend lines, representing the material length required to accommodate the bend. Bend deduction, on the other hand, is the difference between the total flat length of the sheet metal part and the sum of the flange lengths. Both values are essential for determining the accurate flat pattern size required for the bending process.