The System Usability Scale (SUS) gives you the answer of the question "Is my website usable?". Invented in 1986 by John Brooke, it has more than 30 years of use, demonstrating that it is a good method to calculate the usability of your website.
SUS is very easy to administer and very cheap compared with other tests. Is one of the most efficient ways to gathering statistic valid data from users.
Compared with other test, the System Usability Scale is:
- Quicker: Rather than researching and designing a new study, just copy and paste the SUS and start again.
- Cheaper: It is a very short quiz that does not require a lot of software to administer. It is perfect if you do not have enough budget.
Maybe this two benefits gives you the idea of a very poor quality quiz, however it is still valid, you can trust and take data from the users.
The System Usability Scale includes 10 questions which users of your website will answer.
For each question, the user will rank from 1 to 5, based in their level of agreement. 5 means agree completely, 1 means the opposite.
Here are the 10 questions:
- 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.
This image represents an example of questions with the answer:
SUS example question. Source: meiert.com
You need to do some steps to calculate the result of the questionary.
There are some resources to automatise the calculation, for example Excel templates. But I want to explain the entire method because this will provide you better understanding.
Your users ranked from 1 to 5 each of the questions, based on the level of agreement. Take each question and follow this steps:
- For each of the odd numbered questions, subtract 1 from the score.
- For each of the even numbered questions, subtract their value from 5.
- Take these new values which you have found, and add up the total score. Then multiply this by 2.5.
The result of all these calculations is that you now have your score out of 100. This is not a percentage, but it is a clear way of seeing your score.
The average System Usability Scale score is 68, if it is under 68, probably you have usability problems in your website.
If you score is higher than 80, you have website which users probably recommends to others.
51 or under means that you must need to work in usability.
Examples of use
The easiest way to implemente the SUS is to get a clear and quick judgement of the usability of your site:
You have to ask the users:
1- First experience your website.
2- Participate in the SUS.
Also you can compare two different designs. If you have doubts about the layout or style of your website, this method will help you to get very usable information about usability of each design.
You need two groups (one per design), and follow this steps:
Group 1 -> Experience version 1 -> Evaluates version 1 with SUS
Group 2 -> Experience version 2 -> Evaluates version 2 with SUS
The design with higher score wins.
Conclusion and resources
The System Usability Scale and the tests above will help you get a definite grade for the usability of your website. Rather than guessing, you’ll know exactly how well you are doing benchmarked against industry standards.
I recommend this 2 resources to get started: