System Usability Scale (Wikipedia)
An encyclopedia article on the System Usability Scale (SUS): its ten-item structure, scoring formula, and use as a portable, single-number subjective usability measure. Wikipedia articles are continuously edited, so year above reflects the access date (2026-07-13), not a fixed publication year. See Usability Evaluation Methods for SUS’s place among usability-evaluation methods.
License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/
Key points
- Developed by John Brooke at Digital Equipment Corporation in the UK in 1986, originally to assess usability of electronic office systems.
- Ten-item Likert-scale questionnaire (five-point, “Strongly disagree” to “Strongly agree”), alternating positively- and negatively-worded statements to reduce response bias — e.g. “I think that I would like to use this system frequently” alongside “I found the system unnecessarily complex.”
- Scored via a fixed formula — SUS = 2.5 × (20 + sum of odd-numbered item scores − sum of even-numbered item scores) — producing a single 0–100 score, letting outwardly dissimilar systems be compared on one scale.
- The article frames SUS against ISO 9241 Part 11’s usability definition (effectiveness, efficiency, satisfaction, all context-dependent), noting that this context-dependence is exactly why comparing “is system A more usable than system B” is otherwise hard — SUS’s appeal is a sufficiently high-level, general measure that supports the comparison anyway.
- Lewis & Sauro (2009) and Borsci, Federici & Lauriola (2009) independently found the ten items actually load onto two correlated sub-scores, Usability and Learnability, usable separately when that distinction matters.
- Bangor, Kortum & Miller built normative data from a decade of SUS ratings across many systems, and Sauro & Lewis later proposed a curved grading scale mapping mean scores to adjective ratings — the article does not give a single specific “average” score in its current text, only that this normative/grading work exists.