Defect Density

DEFECT DENSITY is the number of confirmed defects detected in software/ component divided by the size of the software/ component.

ISTQB Definition

  • defect density: The number of defects per unit size of a work product.


The ‘defects’ are:

  • confirmed and agreed upon (not just reported).
  • Dropped defects are not counted.

The size is measured in one of the following:

  • Function Points (FP)
  • Source Lines of Code (SLOC)

Defect Density Formula / Calculation

Defect Density = Number of Defects / Size of the Software


  • For comparing the relative number of defects in various software components so that high-risk components can be identified and resources focused towards them.
  • For comparing software/ products so that quality of each software/ product can be quantified and resources focused towards those with low quality.
  • For assessing the performance of software developers. [Take extra caution while using this though; there are many factors involved in their performance and solely using this metric to judge them would be unfair.]

Last Updated on August 31, 2020 by STF