Defect Density

Defect Density Fundamentals


Defect Density is the number of confirmed defects detected in software/component during a defined period of development/operation divided by the size of the software/component.


The ‘defects’ are:

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

The period might be for one of the following:

  • for a duration (say, the first month, the quarter, or the year).
  • for each phase of the software life cycle.
  • for the whole of the software life cycle.

The size is measured in one of the following:

  • Function Points (FP)
  • Source Lines of Code


defect density image


  • 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.