System Usability Scale
Also known as: SUS, System Usability Score
The System Usability Scale (SUS) is a rapid, standardized 10-item questionnaire for measuring perceived system usability in a single summary score. Developed by John Brooke in 1986, SUS has become one of the most widely used post-use usability instruments in industry and research. The scale is administered after a user has interacted with a system, capturing perceived ease of use, learnability, error recovery, and overall satisfaction with a quick, economical assessment that correlates well with comprehensive usability testing.
Key highlights
- Extremely quick and economical; takes 2–3 minutes to administer and score with minimal participant burden.
- Well-validated across industries, platforms, and user populations with decades of normative data.
- Produces a single, interpretable 0–100 score that is easy to communicate to stakeholders and trending over iterations.
- Balanced positive/negative items reduce agreement bias; robust to language and cultural variations.
Intuition
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How it works
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When to use it
Use SUS after users complete task scenarios on a product or prototype. Best applied post-use, when users have direct experience with the system. Most valuable in iterative design cycles where rapid feedback is needed. Useful for benchmarking against industry standards and competitors. Do not rely on SUS alone for identifying specific usability problems; combine with task analysis or think-aloud protocols to locate problem areas.
Strengths & limitations
- Extremely quick and economical; takes 2–3 minutes to administer and score with minimal participant burden.
- Well-validated across industries, platforms, and user populations with decades of normative data.
- Produces a single, interpretable 0–100 score that is easy to communicate to stakeholders and trending over iterations.
- Balanced positive/negative items reduce agreement bias; robust to language and cultural variations.
- Diagnostic power is limited; a low score indicates problems but does not pinpoint where they are.
- Cannot capture task-specific usability concerns; best used alongside task analysis.
- Sensitive to context: post-use emotional state, task difficulty, and user expectations influence scores.
- Sample size of 5–8 participants yields stable scores for comparison, but estimates may vary with small samples.
Common pitfalls
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Applications
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Frequently asked
What sample size do I need for reliable SUS scores?
SUS is stable with as few as 5 participants; 8–10 is standard for design iteration. For robust benchmarking or publication, use 20–30 participants. Statistical power depends on your target effect size and desired confidence.
Can I modify the SUS items for my domain?
Not recommended. The standard 10-item scale is validated and widely benchmarked. Modified versions lose comparability. If you need domain-specific feedback, administer SUS as-is and supplement with custom follow-up questions or other instruments.
How do I interpret changes in SUS scores between iterations?
Changes of 5–10 points are meaningful; below 5 may be measurement noise. Look at item-level changes to identify which aspects improved. Use item analysis (which statements got the most positive/negative responses) to diagnose specific problems.
Sources
- 1.Brooke, J. (1986). System Usability Scale (SUS): A quick and dirty usability scale. In B. Shackel & S. J. Richardson (Eds.), Usability Evaluation in Industry (pp. 189–194). Taylor & Francis.ISBN 0-85066-375-X
- 2.Bangor, A., Kortum, P. T., & Miller, J. T. (2008). An empirical evaluation of the System Usability Scale. International Journal of Human-Computer Interaction, 24(6), 574–594.
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Cite this page
ScholarGate. (2026, June 3). System Usability Scale. ScholarGate. https://scholargate.app/human-computer-interaction/system-usability-scale