// glossary entry

Usability

What is usability?

Usability is the property of a system that enables users to perform defined tasks effectively, efficiently, and satisfactorily (ISO 9241-11). Unlike UX, usability is limited to the system’s functionality; UX also takes into account emotion, expectations, and the user’s overall impression. Usability is measured using the task success rate, time-on-task, error rate, and the SUS questionnaire. At Waterproof Web Wizard, we regularly test usability with short, moderated tests (five users are sufficient in 80 percent of cases) before recommending costly redesigns, often, small adjustments are more effective than major relaunches.

// synonyms

  • Usability
  • Usability
  • ISO 9241
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