# System Usability Scale (SUS)

The System Usability Scale (SUS) provides a “quick and dirty”, reliable tool for measuring 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:

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 questionnaire and scoring are outlined in the [System Usability Scale (SUS) Template](https://www.usability.gov/how-to-and-tools/resources/templates/system-usability-scale-sus.html).

## Interpreting Scores

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](https://www.usability.gov/how-to-and-tools/resources/templates/system-usability-scale-sus.html) provide more information in context about the process.

## References

* [SUS: A Quick and Dirty Usability Scale](http://www.usabilitynet.org/trump/documents/Suschapt.doc) 📷 by John Brooke
* [Measuring Usability with the System Usability Scale (SUS)](http://www.measuringusability.com/sus.php) 📷 by Jeff Sauro
* [SUS: A Retrospective](http://www.upassoc.org/upa_publications/jus/2013february/JUS_Brooke_February_2013.pdf) 📷 by John Brooke
* [Determining What Individual SUS Scores Mean: Adding an Adjective Rating Scale](http://www.usabilityprofessionals.org/upa_publications/jus/2009may/JUS_Bangor_May2009.pdf) 📷 by Kortum Bangor and Miller May