The System Usability Scale (SUS) is a validated ten-item questionnaire that produces a single usability score for any product or service. Created by John Brooke at Digital Equipment Corporation in 1986, it has become one of the most widely used usability measurement tools in the world — partly because it takes under two minutes to complete, partly because decades of published data allow scores to be benchmarked against industry norms and competitor products.

What It Is

The SUS consists of ten statements alternating between positive and negative phrasing. Participants rate each statement on a five-point Likert scale from Strongly Disagree to Strongly Agree. Scores are calculated using a specific formula that converts raw responses to a 0–100 scale. A score above 68 is considered above average; scores above 80 indicate excellent usability. The SUS measures perceived ease of use and learnability simultaneously in a format small enough to include at the end of any usability test.

How to Run It

  1. Administer the standard ten SUS questions immediately after a usability test session — do not modify the wording.
  2. For each odd-numbered question, subtract 1 from the participant's score.
  3. For each even-numbered question, subtract the participant's score from 5.
  4. Sum all converted scores and multiply by 2.5 to get the final SUS score (0–100).
  5. Collect responses from at least ten participants before drawing conclusions.
  6. Benchmark the resulting score against the SUS adjective scale: below 51 is Awful, 68 is OK, above 85 is Excellent.

A SUS score is not a goal in itself — it is a signal that tells you whether to investigate further and where.

When to Use It

Use the SUS after every round of usability testing to track usability improvement across design iterations. It is particularly valuable for competitive benchmarking, stakeholder reporting, and establishing a usability baseline before a redesign project. Add it to remote unmoderated tests to collect usability data at scale without the overhead of qualitative sessions.

Tips for Success

  • Never alter the SUS wording — published benchmarks apply only to the original instrument.
  • Use SUS scores alongside qualitative data: a score of 75 tells you the experience is acceptable but not where to improve it.
  • Track SUS across multiple releases to demonstrate the usability impact of design changes over time.
  • Pair SUS with the Single Ease Question (SEQ) at the task level for a more granular picture of where usability breaks down.