SUS

Purpose

Use the System Usability Scale to measure how usable people perceive a product to be, with a short, standard questionnaire that produces a single score from 0 to 100. John Brooke created it in 1986 as a "quick and dirty" measure. It has since become one of the most widely used usability questionnaires because it is short, free, reliable even with small samples, and comparable across products and over time.

Frameworks & Standards

Item	Value
Framework ID	`sus`
Category	Design and UX — Usability Measurement
Version	2.0.0
Originator	John Brooke
Created / published	1986 / 1996
Benchmark research	Bangor, Kortum & Miller (2008) · Sauro & Lewis

The Instrument

Ten statements, each rated on a five-point scale from strongly disagree to strongly agree.
Items alternate between positive and negative wording to reduce response bias.
Scoring: for odd-numbered items subtract 1 from the response; for even-numbered items subtract the response from 5; add the ten results and multiply by 2.5.
The result runs from 0 to 100 and is not a percentage.

Interpretation. Across large sets of studies, the average score is about 68 (Sauro and Lewis), so scores are best read against that benchmark or as percentiles.

Core Principles

Use the standard wording, or results are not comparable with benchmarks.
It is not a percentage. A score of 68 is roughly average, not 68% usable.
Measures perception, not cause. SUS shows whether there is a problem, not what it is.
Reliable with small samples, which makes it practical for iterative testing.
Compare over time and against benchmarks, not in isolation.

Applications & Use Cases

Use Case	Application	Note
After usability tests	Administer once tasks are complete	Standard practice
Release-over-release tracking	Repeat with the same method	Watch the trend
Comparing designs	Score alternatives with similar users	Same tasks
Benchmarking	Compare against the ~68 average	Use percentiles
Vendor evaluation	Compare tools used for the same job	Consistent tasks
Executive reporting	One simple usability number	With context

Usage Guidelines

Administer after participants have used the product for representative tasks.
Use the original ten items and scale without modification.
Score correctly, applying the odd and even item rules.
Report against the benchmark, with sample size and confidence intervals.
Pair with qualitative findings to explain the score.

Prompt Template

You are measuring usability with SUS (Brooke 1996).

PRODUCT AND TASKS: [[...]]   PARTICIPANTS: n = __
SCORING: odd items (r - 1) · even items (5 - r) · sum x 2.5
MEAN SCORE and confidence interval:
VERSUS BENCHMARK (~68 average):
QUALITATIVE FINDINGS that explain the score:

Ethical Guidelines

Do not present SUS as a percentage or overstate what a small sample shows.

Testing Strategy

Use consistent tasks and participant profiles across rounds.
Report confidence intervals, especially with small samples.

Success Metrics

SUS score trend across releases.
Position relative to the benchmark.

Collaboration Protocol

Inbound from: usability-tester · ux-researcher · product-strategist
Outbound to: ui-designer with the qualitative findings
Cross-framework: Nielsen heuristics identify likely causes; user journey mapping locates problems in the experience.

Related Skills

composable-skills/frameworks/nielsen-heuristics/SKILL.md — finding likely causes
composable-skills/frameworks/user-journey-mapping/SKILL.md — locating problems in the journey
composable-skills/frameworks/ab-testing/SKILL.md — comparing designs rigorously

Reference Materials

Brooke, J. (1996). "SUS: A 'quick and dirty' usability scale." In Jordan, Thomas, Weerdmeester & McClelland (eds.), Usability Evaluation in Industry. Taylor & Francis.
Brooke, J. (2013). "SUS: A Retrospective." Journal of Usability Studies, 8(2), 29–40.
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.
Sauro, J., & Lewis, J.R. Quantifying the User Experience. Morgan Kaufmann (2012; 2nd ed. 2016).

SUS

SKILL.mdcomposable-skills/frameworks/sus/SKILL.md

SUS