What is Defect Severity?

Defect Severity, also called Bug Severity, is a measure of the impact a defect has on the systems's functionality for end-users.

A defect which renders the software incapable of use has the highest severity level while the defects which cause minor inconveniences are on the lower side of the severity scale.

A Quality Assurance engineer usually decides the severity level of a defect.

Severity and Complexity

The severity of a defect should not be confused with its complexity. Sometimes, you can quickly remedy a severe defect while a minor inconvenience may take hours to fix. Severity is purely determined based on how it affects the end-user and has nothing to do with how difficult it is to remedy the defect.

Classification of Defect Severities

You can categorize defects are mainly into the following types:

Critical
A critical defect is a defect that leads to the complete failure of the software system. There are no workarounds. Critical bugs need to be addressed as quickly as possible, as without a fix end-users will not be able to use the application.

For example, on a shopping website like Amazon, the following bugs will be classified as critical:

  • Cannot login into your account.
  • Cannot checkout.
  • Product's price is not displayed.
Major
A major defect is a defect that leads to the failure of a crucial part of the application. Workarounds or alternatives may exist but not ideal.

For example, on a shopping website like Amazon, the following bugs will be categorized as major:

  • Search results do not match the search query.
  • Cannot use debit cards during checkout. (But can use credit cards and other payment options).
  • Product reviews are not displayed.
Minor
A minor defect is a defect that causes problems in some unimportant or niche functionality of the system.

For example, on a shopping website like Amazon, the following bugs will be deemed minor:

  • Cannot search past orders that are more than a year old.
  • Cannot compare more than three products at a time.
  • Thumbnails of product photos uploaded by users are unclear.
Trivial
These defects usually arise in the aesthetic part of the application like misaligned user elements, overlapping text, and links that do not work.

Defect Severity versus Defect Priority

Bug severity often confused with the defect priority. A bug's severity reflects its impact on the end-user, while its priority indicates its effect on the business. For example, a spelling mistake on Amazon's home page would be low severity (since it doesn't affect the end-user) but high priority (since it reflects poorly on Amazon as a company).