SUS: The System Usability Scale

The System Usability Scale (SUS) is a favorite quantitative tool among usability researchers for its simplicity and accuracy. With just 10 questions, a 5-point “Strongly agree” to “Strongly disagree” response system, and a quick scoring algorithm, SUS yields an extremely reliable overall usability score for your website or product on a scale of 0 to 100.

SUS puts your website under the microscope

The questionnaire consists of the following 10 items:

  • I think that I would like to use this system frequently.
  • I found the system unnecessarily complex.
  • I thought the system was easy to use.
  • I think that I would need the support of a technical person to be able to use this system.
  • I found the various functions in this system were well integrated.
  • I thought there was too much inconsistency in this system.
  • I would imagine that most people would learn to use this system very quickly.
  • I found the system very cumbersome to use.
  • I felt very confident using the system.
  • I needed to learn a lot of things before I could get going with this system.

Interpreting your System Usability Scale results

Based on different studies, the mean SUS score is around 68-70.5. Some researchers have attempted to map adjectives like “excellent,” “poor,” or “worst imaginable” to ranges of scores for an additional level of insight. For example, an average score corresponds to the “good” range, but falls short of “excellent.”

With thousands of collected scores to compare to, your raw SUS result can be turned into a percentile ranking, allowing you to contextualize how your site performs relative to many others. Using percentiles, therefore, an average score of 70.5 translates to a 50% – better than half of all other systems tested, and worse than the other half.

SUS System Usability Scale Scores Distribution

Though described by its inventor as a “quick and dirty” measure, studies have found SUS to be among the most accurate and reliable of all usability surveys, across sample sizes. It is now one of the most popular metrics for quantifying system satisfaction, with thousands using it to gauge user-friendliness over a wide range of products online and off.

It is these qualities that make SUS a valuable tool for standardizing a diverse mix of tester feedback, and aggregating responses into a meaningful but concise picture of your UX. If individual test videos are the trees, SUS shows you not only the forest, but the entire ecosystem. With a widely-trusted industry standard to rely on, you can take a step back from your own company and see how you chalk up in the broader world that surrounds you.

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