Glossary
System Usability Scale
What is the System Usability Scale?
The System Usability Scale (SUS) is a ten-item questionnaire about perceived usability. Its answers are combined into a score from 0 to 100.
How is SUS scored?
The standard items use five response options.
- For odd-numbered items, subtract one from the response.
- For even-numbered items, subtract the response from five.
- Add the resulting values and multiply by 2.5.
A SUS score is not a percentage. Reference points such as 68 and letter-grade thresholds come from comparison datasets; they are not universal pass/fail marks.
Example
A team could measure SUS before and after changing its navigation. Comparing the scores is useful, but differences between participants and uncertainty in the estimates also matter. A higher score alone does not establish that the redesign caused the improvement.
Why it matters
SUS gives teams a standard way to ask about perceived usability. Combine it with what users actually accomplish and where they struggle.
John Brooke developed SUS in 1986. The commonly cited chapter, SUS: A Quick and Dirty Usability Scale, appeared in 1996.