The System Usability Scale, often referred to as SUS, is an inexpensive but proven way of effectively measuring the usability of a given product or service. The scale, originally created by John Brooke in 1986, has stood up to a battery of tests over the years and proven itself both reliable and valid. The SUS can be used to evaluate a wide variety of products and services including, but not limited to; hardware, software, mobile devices, websites, and applications.
A product or service’s SUS score is calculated from respondent’s answers to ten simple, Likert scaled questions:

  1. I think that I would use this system frequently.
  2. I found this system unnecessarily complex.
  3. I thought this system was easy to use.
  4. I would need the support of a technical person to be able to use this system.
  5. I found the various function in this system were well integrated.
  6. I thought there was too much inconsistency in this system.
  7. I would imagine that most people would learn to use this system quickly.
  8. I found the system to be cumbersome to use.
  9. I feel very confident using this system.
  10. I needed to learn a lot of things before I could get going with this system.

The answers to these ten questions are rated on a five-point scale, ranging from strongly agree (5) to strongly disagree (1). Scores are calculated by summing the score contributions and multiplying by 2.5. For more detailed information regarding how to calculate SUS scores, check out this article from Usability Geek.

A product or service’s SUS score can be calculated with these ten simple questions, making the test relatively quick and easy for study participants to complete and for researchers to score. Additionally, the System Usability Scale is not trademarked, making it a cost-effective way to evaluate usability. The scale can also be applied to a wide variety of user interfaces and scores are easily understood by individuals from a wide range of disciplines.

The one caveat to using the System Usability Scale is that, often, the gut reaction is to interpret scores as percentages because they range from zero to 100. Unfortunately, this assumption would be incorrect. But, scores can be viewed as percentile rankings, like the standard letter grade scale – which most people are familiar with. Research has also shown SUS scores correlate with certain adjective ratings, which has helped practitioners communicate the meaning of individual SUS scores. Here are some examples:

The System Usability Scale is an inexpensive but effective way of measuring the usability of your company’s products or services. While collecting the data may seem easy enough, the quality of your results will depend entirely on the quality of your data collection methodology. Additionally, for those less experienced with SUS scores, it can be difficult to generate meaning from raw scores. This is why it’s essential to work with experienced professionals, especially when it is in regards to something as important to your company’s success as usability.

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Also published on Medium.