Quantifying feedback from a usability survey.
System Usability Scale (SUS)
The System Usability Scale (SUS) provides a “quick and dirty”, reliable tool for measuring the usability. It consists of a 10 item questionnaire with five response options for respondents; from Strongly agree to Strongly disagree. Originally created by John Brooke in 1986, it allows you to evaluate a wide variety of products and services, including hardware, software, mobile devices, websites and applications.
Benefits of using a SUS
SUS has become an industry standard, with references in over 1300 articles and publications. The noted benefits of using SUS include that it:
Is a very easy scale to administer to participants
Can be used on small sample sizes with reliable results
Is valid – it can effectively differentiate between usable and unusable systems
Considerations when using a SUS
If you are considering using a SUS, keep the following in mind:
The scoring system is somewhat complex
There is a temptation, when you look at the scores, since they are on a scale of 0-100, to interpret them as percentages, they are not
The best way to interpret your results involves “normalizing” the scores to produce a percentile ranking
SUS is not diagnostic – its use is in classifying the ease of use of the site, application or environment being tested
The System Usability Scale
When a SUS is used, participants are asked to score the following 10 items with one of five responses that range from Strongly Agree to Strongly disagree:
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.
The questionnaire and scoring are outlined in the System Usability Scale (SUS) Template.
Interpreting scoring can be complex. The participant’s scores for each question are converted to a new number, added together and then multiplied by 2.5 to convert the original scores of 0-40 to 0-100. Though the scores are 0-100, these are not percentages and should be considered only in terms of their percentile ranking.
Based on research, a SUS score above a 68 would be considered above average and anything below 68 is below average, however the best way to interpret your results involves “normalizing” the scores to produce a percentile ranking.
The references at the end of this page and the template provide more information in context about the process.
SUS: A Quick and Dirty Usability Scale Site exit disclaimer by John Brooke
Measuring Usability with the System Usability Scale (SUS) Site exit disclaimer by Jeff Sauro
SUS: A Retrospective Site exit disclaimer by John Brooke
Determining What Individual SUS Scores Mean: Adding an Adjective Rating Scale Site exit disclaimer by Kortum Bangor and Miller May