System usability score (SUS)

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The System Usability Scale (SUS) is a 10-item Likert scale questionnaire that provides an at-a-glance look at the ease of use (or lack thereof) of websites, software, hardware, mobile devices, and other technological applications. Respondents rank each statement on a scale of 1 (strongly disagree) to 5 (strongly agree).

There isn't one single aspect of usability when it comes to creating a usable product or system. The SUS helps you measure a combination of factors, including:

• Efficiency: How fast someone can use it

• Intuitiveness: How effortlessly someone can understand it

• Ease: How simple it is to use

• Satisfaction: How much a user subjectively likes or dislikes using it

SUS can be used for products, websites, applications, hardware, software, and more.

Measuring SUS

1. measures a product’s usability—or, more specifically, the end user’s perception of how usable and user-friendly the product is.

2. informs how users rate the usability of your designs, asking them to score factors such as the ease, learnability, and consistency of your UX

3. To measure system usability, you’ll first run a usability test. At the end of the test, you’ll ask your participants to complete the SUS questionnaire—a list of 10 items which they’ll rate with a choice of answers ranging from “strongly agree” to “strongly disagree.”

   1. Based on your users’ answers, you’ll then calculate an SUS score. This can be a bit tricky, but here are the steps you’ll need to follow:

      • Strongly disagree: 1 point

      • Disagree: 2 points

      • Neutral: 3 points

      • Agree: 4 points

      • Strongly agree: 5 points

   2. Add up the user’s score for all odd-numbered questions (i.e. questions 1, 3, 5, 7, and 9 on the questionnaire), then subtract 5. This will give you the value of X.

      1. Add up the user’s score for all even-numbered questions (i.e. questions 2, 4, 6, 8, and 10), then subtract that number from 25. This will give you the value of Y.

      2. Add X and Y, then multiply this new value by 2.5. That’s your final system usability score. Research suggests that a usability score of 68 or higher is considered above-average. Use that to benchmark and interpret your findings.  

4. set task test then test with users. Define questions and then ask users.

SUS Benefits

• It provides an at-a-glance snapshot of how usable or unusable your system is.

• It's easy to use, at scale or with a small number of respondents.

• It can be repeated for many different products and systems.

• Established over decades

SUS Limitations

• Limited assessment of user behaviour

• Opinionated and subjective

• Ideally should be supported by other research method

• No why the user answered a question with the value

Example SUS questionnaire

1. I think that I would like to use this software frequently.

2. I found this software unnecessarily complex.

3. I thought this software was easy to use.

4. I think that I would need assistance to be able to use this software.

5. I found the various functions in this software were well integrated.

6. I thought there was too much inconsistency in this software.

7. I would imagine that most people would learn to use this software very quickly.

8. I found this software very cumbersome/awkward to use.

9. I felt very confident using this software.

10. I needed to learn a lot of things before I could get going with this software.

Sources

• https://blog.hubspot.com/service/system-usability-scale-sus

• https://www.eleken.co/blog-posts/ux-design-kpi-examples-learn-how-to-measure-user-experience

• https://www.testingtime.com/en/blog/important-ux-kpis/

• https://www.uxdesigninstitute.com/blog/ux-kpis-and-how-to-measure-them/