K Factor in sheet metal bending is a constant used to calculate sheet metal flat length or Flat-pattern. Mathematically k factor value is equal to the ratio of position of neutral axis and sheet thickness. During sheet metal part bending, the inside bending surface is compressed, whereas the outer surface is stretched. 

this image indicates the position of neutral axis when sheet metal is bend.
Neutral Axis Representation
This image indicates bend allowance in sheet metal parts.
Sheet Metal Bend Allowance

As shown in above image, due to compression and tension in sheet metal part, overall sheet metal part length increases. This change in sheet length depends on the position of neutral axis in the sheet metal part and the position of  neutral axis depends on the value of k-factor.  For more details on K-factor we suggest you also read this article on k-factor and flat pattern calculations.

How to calculate the value of K Factor

Best way to calculate the value of k factor in sheet metal is by reverse engineering. You can use this K-Factor calculator to calculate k factor using reverse engineering approach.

Afterwards k-factor is used in CAD software to calculate sheet-metal blank size from cad design. You can also use our flat pattern calculator for blank size calculation.

How to use This K-Factor Calculator in Sheet Metal

(Reverse Engineering Approach)

K-factor in sheet metal can be calculated in following steps.


Cut a sample sheet and measure it’s total flat length and sheet thickness in mm. Strip width is not very critical.


Bend the sheet to 90 degrees and measure length A and B.

(Please note the bending of the sample part is done in the same manner as we are planning for production. Because different machines and bending tools give different k factor values.)


Value of the inside bend radius depends on the bending tool and die. Generally it is considered equal to sheet thickness.

K Factor Calculator

Facts about K-Factor

  • Inside compression in sheet metal cannot exceed the outside tension. Therefore k-factor value can not exceed “0.5” .
  • Neutral axis cannot go beyond the middle of the sheet thickness.
  • K factor Value is inversely proportional to sheet thickness. Increase in thickness, decreases k-factor value.
  • K-factor value is inversely proportional to material hardness. Therefore with Increase in hardness, K factor value decreases .

To sum up, This calculator can be used to calculate sheet metal K-Factor using reverse engineering method. This k factor is used to calculate sheet metal flat length. 

We will keep adding more information on sheet metal K Factor calculator. Please share your suggestions, comments or questions on sheet metal k factor in the comment box.

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