Logo for usabiliTEST System Usability Scale Plus (SUS+) tool

System Usability Scale (SUS) Plus


What is SUS and how it can help you improve usability of your product?

Logo for usabiliTEST System Usability Scale Plus (SUS+) tool Original System Usability Scale, also known by its abbreviation as SUS was developed by John Brooke in 1986, it allows you to evaluate a wide variety of products and services, including hardware, software, mobile devices and websites. It is a simple, ten-item Likert scale with five response options for respondents; from Strongly agree to Strongly disagree. It provides an efficient and reliable research tool for measuring the usability and works really well alongside other user testing tools. And while the SUS is often referred to as an “industry standard” in the business and technology industries Brooke himself has noted “it has never been through any formal standardization process”. This tool allows us to measure and quantify the perception of usability by your users.

Below are the ten statements on the survey:
  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.
  6. I thought there was too much inconsistency in this system.
  7. I would imagine that most people would learn to use this system very quickly.
  8. I found the system very cumbersome to use.
  9. I felt very confident using the system.
  10. I needed to learn a lot of things before I could get going with this system.
It is important to note that the order in which SUS questionnaire statements appear is intentional and should not be changed to make sure the score is calculated properly.

SUS is particularly relevant to user experience when you want to compare two versions of an application that are based around different technologies. It allows you to make that comparison, at least as far as perceived usability goes. Because SUS is pretty much technology-neutral, you can continue to use it in usability testing as technology evolves over the years, and you don’t have to continually reinvent questionnaires.


SUS scoring

Our online version of SUS tool has a built-in score calculator and the data is analyzed in real-time, producing instant and easy to read values.

However, if you are wondering how SUS calculator works, here's a quick overview. As mentioned above, SUS survey consists of 10 statements and each one is presented in a form of a Likert five point scale, ranging from 1 to 5. The odd numbered questions express positive attitudes, while the even ones - negative. In order to calculate SUS score you subtract 1 from the user responses to odd statements, and subtract corresponding values from 5 in the even-numbered statements. At this point the converted response scale will be ranging from 0 to 4 with four being the most positive. By adding responses from all participants and multiplying the total by 2.5 converts the range from 0-40 to 0-100.

It is important to note that raw scores are not expressed as percentages and must be normalized to produce a percentile ranking.

SUS Score Letter Grade Adjective Rating
Above 80.3 A Exellent
Between 68 and 80.3 B Good
68 C OK
Between 51 and 67 D Poor
Below 51 F Awful
In addition, analyzed results produce the report with the following values:

US scores can be translated into letter grades, which may be helpful for communicating results to stakeholders.

Screenshot of summary panel for a System Usability Scale project
Screenshot of usabiliTEST's results summary page.

Why "Plus" in the name?

usabiliTEST's online SUS version of the tool is called SUS Plus, because it offers two additional options, that can ge enabled together or separately:

  • Adjective Rating Scale
  • Promoter Rating Scale

Adjective Rating Scale was added in order to help answer the question: "What is the absolute usability associated with any individual SUS score?". It is an optional eleventh question to the SUS. However, instead of following the SUS format, a seven-point, adjective-anchored Likert scale was used to determine if a word or phrase could be associated with a small range of SUS scores. There is a very strong correlation between the two.

Promoter Rating Scale is based on Net Promoter Score® (NPS®), a management tool that can be used to gauge the loyalty of a firm's customer relationships, developed by (and a registered trademark of) Fred Reichheld, Bain & Company, and Satmetrix Systems. The score is calculated based on responses to a single question: How likely is it that you would recommend our company/product/service to a friend or colleague? Unlike SUS, which measures the perception of usability of your product, Net Promoter Score is measuring the loyalty of customers towards your brand.

FAQ

Is SUS+ test available in different languages?

Yes, you can now launch your SUS+ test in one of the following languages:
  • English
  • French
  • German
  • Portuguese
  • Spanish
  • Simplified Chinese

How do you use SUS?

Because SUS is technology-independent it is a reliable tool for measuring usability. Gauging users perception of your product is the best way to improve it.

What is an average SUS score?

Score of 68 and above is considered to be good, while below 68 indicated that there's more work needed to improve usability.
Source: FAQ #sus

Acknowledgments

SUS was developed as part of the usability engineering program in integrated office systems development at Digital Equipment Co Ltd., Reading, United Kingdom.

  • Brooke, J B (1996). SUS - a quick and dirty usability scale. In: ‘Usability Evaluation in Industry’, Jordan, P, Thomas, B, Weerdmeester, B, and McLelland, I (eds). Taylor and Francis: London.
  • Brooke, J B (2013). SUS – a retrospective. Journal of Usability Studies, Vol. 8, Issue 2, February 2013 pp. 29-40.
  • Bangor, A., Miller, J. & Kortum, P. (2009). Determining what individual SUS scores mean: Adding an adjective rating scale. Journal of Usability Studies, 4(3), 114–123.

Blog articles

What Is the System Usability Scale (SUS) and Why Is It Important?

The system usability scale (SUS) is a great way to evaluate the usability of your product. Learn more about the SUS here.

Making Sense of SUS Data

Providing an assessment tool to determine the ease and usability of your website and technological apps, let's break down SUS and how to use it.

Multilingual SUS PDF generator

Free tool

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Conducting SUS evaluation offline? Create print-ready System Usability Scale questionnaire for your participants with our SUS PDF generator. This tool is multilingual and is capable of producing SUS questionnaire in English, German, French, Portuguese and Spanish languages.