Usability Testing Feb 26, 2020

Measure Usability with the System Usability Scale (SUS)

Measure Usability with the System Usability Scale (SUS)
Usability Testing Feb 26, 2020

“Quick and Dirty”: Quick - Yes, Dirty - No, SUS is absolutely not dirty.

It has stood the test of time and proven itself valuable everytime we have used it.


To evaluate a wide variety of products and services, including hardware, software, mobile devices, websites and applications, System Usability Scale (SUS) has been used. Already established as an industry standard, SUS is referenced in thousands of articles and research papers.


Easy, Valid and Reliable even on small sample sizes, SUS is a Usability metric of choice at enterprise and startups alike. Easy both for the Researchers and the Participant to respond, the SUS is 10 simple multiple choice questions. The questions are presented to the Respondents after they have used the Product. This could be Mobile App, Website, etc.


The Participants provide their option to each of the following 10 statements with a single response from the scale - Strongly Agree (1) to Strongly disagree (5):


  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.


The above ten statements are actually alternating, between positive statements and negative statements. It's worth advising your respondents to not think for too long before answering to each statement. In case you believe that respondents might be confused with uage of the word "system" in the statements, you can choose to replace "system" with "product".


The scores are calculated based on rating of the responses from Participants. To calculate, follow the steps below:

  • For odd numbered items above (1, 3, 5, 7, 9): subtract one from the Participant’s response.
  • For even-numbered items above (2, 4, 6, 8, 10): subtract the Participant’s responses from 5. 
  • Now that every answer will convert all values to be 4 or less than 4. Total up the converted responses for each Participant.
  • Multiply the total by 2.5. The resulting range of possible values would be converted to a range ‘0 to 100’.


How to interpret the SUS Scores

UXArmy user testing platform includes automatic SUS calculation. Researchers can add SUS with a single click during the creation of your User Test. Going by the existing literature and our own experience doing Usability testing with several corporations in Asia, a SUS score below 68 can be considered below average Usability. 68 by no means implies that Usability is 68%, it’s in fact just represents an average usability.


‘SUS Reporting’ screenshots from UXArmy Remote User Testing platform


The SUS was developed by John Brooke in 1986, and since then has gained significant usage in the industry and academia. SUS is not diagnostic”. What does that mean? Using SUS to find usability problems is a misconception; it's simply not built for that. As far as Researchers use SUS as an additional indication of perceived Usability of participants towards a certain product, it can help you identify the need to improve usability of your product.


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