System Usability Scale (SUS)
A 10-item standardized questionnaire that produces a score from 0-100 measuring perceived usability. The industry's most widely used instrument for benchmarking usability.
Definition: A 10-item standardized questionnaire that produces a score from 0-100 measuring perceived usability. The industry's most widely used instrument for benchmarking usability.
The System Usability Scale (SUS), developed by John Brooke in 1996, is the industry's workhorse for measuring perceived usability. It is quick, reliable, and has decades of benchmark data available.
How It Works
SUS consists of 10 simple statements that users rate on a 5-point scale from "Strongly Disagree" to "Strongly Agree." The responses are converted to a score from 0 to 100.
Interpreting Scores
Based on extensive research and benchmarking:
- Above 85: Excellent usability
- Above 71: Good usability
- 50-70: Acceptable but room for improvement
- Below 50: Poor usability requiring attention
These thresholds come from large-scale studies that established what scores mean in practice.
Why SUS Works
Technology-agnostic: Works for any interactive system—software, hardware, websites, apps
Standardized: Validated for reliability; produces consistent results
Benchmarkable: Massive public datasets allow comparison to industry averages
Quick: Takes about one minute to complete
Important Notes
SUS measures perceived usability, not actual performance. A user might rate a product highly even if they struggled, or rate it poorly despite succeeding. Combine SUS with objective metrics (task success, time on task) for a complete picture.
Do not change the wording of SUS questions—this invalidates comparison to benchmarks.
Related Terms
Usability
Per ISO 9241-11: the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use.
Psychometrics
The science of measuring psychological constructs—attitudes, abilities, personality traits—through standardized instruments. The discipline behind every validated questionnaire in UX research.
UX Test
A Core Method combining all three Building Blocks: testing task completion (effectiveness and efficiency), observing behavior and non-verbal cues, and asking questions about the experience. The most comprehensive single research method.
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This term is referenced in the following articles:
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