What Is System Usability Scale (SUS)?

It is a questionnaire that helps testers objectively assess the usability of systems. SUS is based on a list of 10 questions with five variants to answer.

This questionnaire was developed by John Brook at Digital Equipment Corporation in the UK in 1986 as a tool for evaluating the usability of an electronic office system.

10 Questions To Answer

1. I think I would like to use this system often
2. I find this system unnecessarily complex
3. I think the system is easy to use
4. I think I will need technical support to be able to use this system
5. I have found that the various functions in this system are logically integrated
6. I think there are too many inconsistencies in this system
7. I believe that most people would learn to use this system very quickly
8. I find this system very cumbersome to use
9. I felt very confident using the system
10. I had a lot to learn before I started to work with this system

All the answers are represented as an opinion scale with 5 options, where 1 is for Strongly Disagree and 5 is for Strongly Agree.

How To Interpret Scores

Here is a framework for calculating the final SUS score.

• For all odd numbered questions, add up their total score and then subtract one from it. That is your X.
• For each of the even numbered questions, add up their score and substract that total from 25. That is your Y.
• Add up X and Y, multiply this sun by 2,5.
  

The average SUS score is 68. Thus, a SUS score above 68 is considered above average and good, and a score below 68 is considered below average.

The best way to interpret this result is to convert it to evaluate the SUS results in terms of which score is acceptable and which one signals critical problems. For example, if you have less than 50 points, you should reconsider your design.

You can also formalize this approach by categories. For example, you can use grades. In this system, design with F or D needs some improvements.