Textbook of Usability

Also known as: SUS

The System Usability Scale (SUS) is a 10-item standardised questionnaire developed by John Brooke in 1986 for quickly measuring subjective usability. Its brevity, ease of administration, and widely published benchmarks have made it the most popular usability questionnaire in the world.

The 10 items alternate between positive and negative statements, rated on a 5-point Likert scale from "Strongly disagree" to "Strongly agree". Examples:

1. I think that I would like to use this system frequently.
2. I found the system unnecessarily complex.
3. I thought the system was easy to use.
4. I think that I would need the support of a technical person to be able to use this system.
5. I found the various functions in this system were well integrated.

Scoring produces a single number from 0 to 100. The formula subtracts 1 from odd-item scores and subtracts even-item scores from 5, sums the results, then multiplies by 2.5.

Benchmark interpretations (from Sauro & Lewis, Quantifying the User Experience):

• > 80.3: Excellent (top 10% of systems)
• 68–80.3: Good (above average)
• 68: Average
• 51–68: Below average
• < 51: Poor (bottom quartile)

The SUS is not diagnostic — it does not say why usability is good or bad — but it provides a comparable metric across systems, versions, and time. A single number is easy to report to stakeholders and track across releases. It remains the standard against which most newer usability questionnaires are compared.