What is System Usability Scale?
The System Usability Scale (SUS) is a 10-item questionnaire that provides a quick, reliable measure of perceived usability, yielding a single score from 0 to 100.
How it works
Developed by John Brooke in 1986, SUS alternates positively and negatively worded statements (‘I found the system unnecessarily complex,’ ‘I felt very confident using the system’) rated on 5-point Likert scales. The scoring formula accounts for the alternating valence and produces a composite score. A SUS score above 68 is considered above average; above 80.3 is Grade A. SUS has been validated across thousands of studies and can be compared across different products and industries because it measures general usability perception rather than domain-specific attributes. Its brevity (10 items, 2 minutes to complete) makes it easy to administer after usability testing or as a periodic benchmark.
Applied example
A SaaS product conducts quarterly SUS measurements. After a navigation redesign, SUS jumps from 62 (below average) to 78 (above average), providing a standardized metric that demonstrates the redesign’s impact to stakeholders who do not attend usability sessions.
Why it matters
The System Usability Scale provides a standardized, comparable, and well-validated measure of perceived usability that enables benchmarking across products, versions, and time periods.
