What is SUS
SUS stands for “system usability scale”. It’s a tool to measure the ease of use of websites and digital products, therefore helping UX specialists to determine flaws in their designs based on the users' feedback. The SUS has also proven to be one of the most efficient ways to collect statistically meaningful data.
Of course, when you conduct user tests it is always insightful to have interviews with participants, ask them open questions and get a detailed feedback. But what if you do testings so frequently that you (or your users) simply don't have time for long conversations? Or if you want to measure your design’s usability quantitatively?
Yes, you can spend time on creating your own questionnaire. Why reinvent the wheel though if there is a scale that has been validated and is easy to apply?
Furthermore, if your job requires to test designs on a regular basis, such a quantitative measurement allows to easily track progress across versions of your design, as well as assign a certain quality standard to them. It's an easy for understanding evaluation to keep your stakeholders up to date.
Another advantage of using SUS in user tests is the possibility to use it as a comparison point for AB tests of your prototypes. For example, it can be done by splitting all participants in two halves and exposing them 50:50 to two different designs. You can then use the SUS score for each design as a means to determine which version performs best.
If you want to go directly to calculating the score, here is the SUS calculator built by weave.ly. It will let you take a test straight away and will instantly show the result.
How to use SUS
The SUS is a survey that consists of ten 5-point Likert scale questions (from strongly agree to strongly disagree).
Below you can see a template with 10 standard questions typically asked during the testing. Of course, it is possible to further tweak the questions for a specific project.
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 product 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.
Concerning the sample size, we would recommend to have around 8-12 participants for more reliable results (although technically this ideally depends on the total size of your population). Also, remember that half of the statements should be positively worded whereas the other half has to be worded negatively.
How to calculate the SUS score
The set-up of the test using SUS is pretty straightforward. However, the complicated part starts when you get to interpreting the scores. Yes, doing these calculations manually is not rocket science, but it may be time consuming and confusing.
We won't go into much detail about formulas here, instead we will show how to automate the process by setting the SUS and calculating the score in a few clicks with no code. If you are still curious and would like to learn how to do calculations manually, in this blog you can find useful information on how to apply the formula.
How to create an SUS questionnaire and calculate the SUS score automatically
Surprisingly, the number of tools that offer full automation with respect to setting up an SUS questionnaire and calculating the scores is limited.
The tools we'll be talking about in this section differ in the extent of automation they provide.
Google Forms & Excel
One of the most popular approaches is launching an SUS questionnaire in Google forms, exporting responses to Excel and automating calculations in the spreadsheet. Here you can find a ready-to-go SUS questionnaire made in Google Forms. It is far from perfect if you want your survey to have a more custom look, yet something you can deploy quickly and easily. This is a Google Sheets spreadsheet for calculating the score.
UserTesting is a user research platform but it also has a separate app that allows for adding the SUS into any test set up within the UserTesign platform.
This approach requires much less effort than Google Forms + Excel/Google spreadsheets combination, as the SUS questionnaire is already created for you. The app enables response collection and then calculates the SUS score for you.
It's easy to set up the questionnaire. The only thing you need to do is to enter the term you want to use to refer to your design, such as system, product, site, app, etc. It will be then included in each question.
Speaking of downsides, the SUSplus tests are not available on mobile devices. You should also bear in mind that UserTesting is a paid service, and the app is only available with a subscription.
If you're a UX designer that is used to creating custom questionnaires in a particular design tool like Figma, you might face a very limited customisation in UserTesting. Although questionnaires created in this tool look more professional than the ones made with Google Forms, there is still practically nothing you can change in terms of design.
Weave.ly is a code-free prototyping tool that operates as a plugin for Figma and turns designs into working web apps. Launching forms designed in Figma and collecting responses is also one of weave.ly's basic features.
There are two ways you can build and launch a SUS questionnaire with weave.ly.
The first option
Use the pre-built SUS calculator (built with weave.ly), which offers a ready-to-use questionnaire. You can send the link to individual users, their response will be collected and the score will be calculated automatically. Yet, there is one limitation.
At the moment you can’t collect the scores calculated for each respondent. You’ll need to either be present (e.g. in a moderated setting) or ask the respondents for the score. But: the weave.ly platform considers making this feasible if there is a high demand for such a tool.
At the moment, it is a "bilateral" procedure. A designer sends the questionnaire form to the user and receives this user's score. This can be repeated as many times as you want if you have a large sample size.
The second option
Is for those who prefers more custom-looking designs. Since weave.ly integrates with Figma, you can first design an SUS survey directly in the design tool. Then, with the help of the plugin you'll need to assign functionalities to a design and turn it into a web app to collect responses. This method might take more time, but is really convenient if you're a regular Figma user.
So, once having prepared a design in Figma, tag elements of your questionnaire with desired functionality, apply a formula used to calculate the SUS score (you don't need to do any calculations yourself), publish the web app and collect submissions. As easy as that!
This way, you can publish the questionnaire as your own project, send the link to as many test participants as you want and collect data summarised in comprehensive data tables, with the scores being calculated of course.
All the features are available for free, as well as a bunch of tutorials in the weave.ly academy to help you quickly learn how to use the platform.
Download the plugin here.
What is a good SUS score
The first thing to remember when interpreting the scores is that although the score scale ranges from 0 to 100, it is NOT a percentage.
An average score is considered to be 68 which equals a grade "B" or simply means "good". A score of 80 or higher is considered to be excellent.
80.3 or higher is an A — The usability of your product was highly appreciated.
From 68 to 80.3 is a B — Good result, you did a great job.
From 51 to 68 equals a C — It's not at all bad, but there's definitely a room for improvement.
51 and below is an F — Such a score indicates that you do have problems with usability that must be fixed.