What is Defect Density? Formula to calculate with Example

Software is tested based on its quality, scalability, features, security, and performance, including other essential elements. It's common to detect defects and errors in a software testing process. However, developers must ensure they are taken care of before launching it to the end-users. This is because fixing an error at an early stage will cost significantly less than rectifying it at a later stage.

The process of defect detection ensures developers that the end product comprises all the standards and demands of the client. To ensure the perfection of software, software engineers follow the defect density formula to determine the quality of the software.

More Defects = Lower Quality

What is Defect Density in software testing

Defect density is numerical data that determines the number of defects detected in software or component during a specific development period. It is then divided by the size of the software. In short, it is used to ensure whether the software is released or not.

The role of defect density is extremely important in Software Development Life Cycle (SDLC). First, it is used to identify the number of defects in software. Second, this gives the testing team to recruit an additional inspection team for re-engineering and replacements.

Defect density also makes it easier for developers to identify components prone to defects in the future. As a result, it allows testers to focus on the right areas and give the best investment return at limited resources.

How to Calculate Defect Density?

The defect density is calculated by dividing the 'total defects' of software by its 'Size.'

Defect Density = Total Defect/Size

According to best practices, one defect per 1000 lines (LOC) is considered good. Such standard of defect density is called KLOC. The size of the software or code is expressed in Function Points (FP).

Steps to calculate Defect Density −

Collect the total defects detected during the software development process

Calculate Defect Density = Average number of Defects/KLOC

Let's understand it with an example −

Let's say your software comes with five integrated modules.

  • Module 1 = 5 bugs

  • Module 2= 10 bugs

  • Module 3= 20 bugs

  • Module 4= 15 bugs

  • Module 5= 5 bugs

  • Total bugs = 5+10+20+15+5= 55

Now total line of code for each module is

  • Module 1= 500 LOC

  • Module 2= 1000 LOC

  • Module 3= 1500 LOC

  • Module 4= 1500 LOC

  • Module 5= 1000 LOC

Total Line of Code = 500 + 1000 + 1500 + 1500 + 1000 = 5500

Defect Density = 55/5500 = 0.01 defects/LOC or 10 defects/KLOC

Uses of Defect Density

Defect density is considered an industry standard for software and its component development. It comprises a development process to calculate the number of defects allowing developers to determine the weak areas that require robust testing.

Organizations also prefer defect density to release a product subsequently and compare them in terms of performance, security, quality, scalability, etc. Once defects are tracked, developers start to make changes to reduce those defects. The defect density process helps developers to determine how a reduction affects the software quality-wise.

The use of defect density is inconsiderable in many ways. However, once developers set up common defects, they can use this model to predict the remaining defects. Using this method, developers can establish a database of common defect densities to determine the productivity and quality of the product.

Factors Affecting Defect Density Metrics

As we know, defect density is measured by dividing total defects by the size of the software. The goal is not about detecting the defects but to detect defects that actually matter. Therefore, it's crucial to understand the factors that result in an efficient outcome. Developers and the testing team need to arrange all the necessary conditions before initiating this process. This helps developers trace the affected areas properly, allowing them to achieve highly accurate results.

Factors that affect defect density are −

  • Types of defects

  • Critical and complexity of the code used

  • Skills of the developer and testing team

  • Time allocated to calculate the defect density

Above all, the efficiency and performance of the software remain the biggest factor that affects the defect density process.

Advantages of Defect Density

Defect density comes with several benefits for software testers and developers. Apart from providing exceptional accuracy in defect measurements, it also caters to many technical and analytical requirements. Having accurate results at hand can help software engineers stay confident about their developed software's quality and performance.

Several other advantages of defect density include −

  • Developers can ensure that the product set to launch doesn't require any more testing

  • Developers and testers can estimate the testing and rework required to fix the errors

  • Testers can trace and detect components possessing high risks

  • The testing team can determine the amount of training requires to complete the testing process

  • One can identify the area of improvement and fix it


Defect density is considered one of the most efficient testing techniques in the overall process of the software development process. While this practice is considered unnecessary by some software engineers, but it is still revered as the best way to identify bugs and errors in software.


What is a Defect Based Software Testing Technique?

The defect-based testing technique is used to prepare test cases based on defects detected in a product. This process doesn't consider the specification-based techniques that follow use cases and documents. Instead, in this strategy, testers prepare their test cases based on the defects.

This technique can be conducted along with test deriving conditions and used to enhance testing coverage. It can also be used once testers identify all test conditions and test cases to gain additional insight into the whole testing process.

When to use a defect-based technique in software testing?

Although one can use the defect-based technique at any level of testing, most testers preferred it during systems testing. This is because testers can base their test cases on defect taxonomies and root cause analysis.

How to write test cases using defect-based testing techniques?

The defect testing technique is written using a 5 step plan −

  • Identify your requirements

  • Accumulate all the defects

  • Apply skills to analyze the defects

  • Find a link between the defects with the requirement

  • Use the linked defects to write your test conditions or cases