Value Metric
System Usability Scale (SUS)
The System Usability Scale (SUS) is a standardized 10-item questionnaire that scores perceived usability from 0 to 100.
What is System Usability Scale (SUS)?
The System Usability Scale is a 10-question survey, alternating positive and negative statements, that respondents rate from strongly disagree to strongly agree. A simple scoring procedure converts the answers to a single number from 0 to 100. Because it is standardized and industry-tested, SUS lets you benchmark perceived usability across products, versions, and time.
SUS is deliberately quick and technology-agnostic, which is why it has become the most widely used usability questionnaire in the field.
How to calculate it
SUS = (Σ adjusted item scores) × 2.5, on a 0–100 scale
- Odd items
- Score contribution = response − 1
- Even items
- Score contribution = 5 − response
Worked example
Sum the adjusted scores of all 10 items (each 0–4, max 40), then multiply by 2.5. An adjusted sum of 32 gives a SUS of 32 × 2.5 = 80.
What good looks like
- Average / good~68 average · 80+ excellent
A SUS around 68 is the long-run average; scores above 80 place a product in roughly the top tier of usability.
Source: MeasuringU (Jeff Sauro)
Why it matters
SUS gives you a fast, comparable read on whether people find your product usable, without a large research operation. Its standardization is the point: a SUS of 78 means something relative to the 68 average and to your last release. It measures perception, though, so pair it with behavioral usability metrics for a complete picture.
How to improve System Usability Scale (SUS)
Find and fix usability failures
Run task-based usability tests to locate the specific problems dragging perceived usability down.
Re-measure after each iteration
Track SUS release over release so you can tell whether changes actually improved perceived usability.
Frequently asked questions
What is a good SUS score?
The long-run average SUS is about 68, so scores above that are above average. A SUS above 80 generally indicates excellent perceived usability, placing the product in roughly the top tier. Because the scale is standardized, these benchmarks hold across product types.
Is a SUS score a percentage?
No — despite ranging 0–100, SUS is not a percentage or a percentile. A 68 does not mean "68% usable." To express SUS as a percentile rank against other products, it must be converted using published norms.