What's the System Usability Scale (SUS) & How Can You Use It?

When I think of a product that likely scores high on the System Usability Scale (SUS), I think of my PopSocket.

I simply attach the Slidable Grip onto my phone within seconds and — voila. I have a phone grip, so I don't drop my phone, and a mount that allows me to prop my phone up to watch anything I want.

Usability is important when it comes to customer satisfaction. Let's face it: If a product is hard to use, you probably wouldn't like it very much. In this article, we'll talk more about usability and how you can measure it using the System Usability Scale.

User-centered design helps product managers, designers, and engineers prioritize the user experience to help make the end-product as usable as possible.

User testing over the course of product development can help make usability improvements that will benefit the end user, and the System Usability Scale (SUS) is one form of user testing you can implement.

The System Usability Scale was created by John Brooke in 1986 to measure the usability of electronic office systems, but it's now applied to a wide variety of web or technology-based applications to measure how easy or difficult they are to use in order to improve.

There isn't one single aspect of usability when it comes to creating a usable product or system. But as shown in the image above, the SUS helps you measure a combination of factors, including:

• Efficiency: How fast someone can use it
• Intuitiveness: How effortlessly someone can understand it
• Ease: How simple it is to use
• Satisfaction: How much a user subjectively likes or dislikes using it

System Usability Scale Questions

The System Usability Scale consists of the following 10 questions that can be answered on a five-point Likert scale of 'Strongly Disagree' to 'Strongly Agree'.

In this example, we'll reference a website in the context of the questions, but the SUS can be used for products, websites, applications, hardware, software, and more.

Here's what the SUS questions would look like for that website:

1. I think that I would like to use this website frequently.
2. I found this website unnecessarily complex.
3. I thought this website was easy to use.
4. I think that I would need assistance to be able to use this website.
5. I found the various functions in this website were well integrated.
6. I thought there was too much inconsistency in this website.
7. I would imagine that most people would learn to use this website very quickly.
8. I found this website very cumbersome/awkward to use.
9. I felt very confident using this website.
10. I needed to learn a lot of things before I could get going with this website.

These questions ask, with a variety of different phrasing and nuance, questions about how easy or difficult it is to use whatever tool users are being surveyed about.

Next up, we'll discuss the SUS scoring process.

System Usability Scale Scoring

There are two parts to the SUS scoring process. The first is to calculate your score. Then, once you have your final score it's important to understand what it means in the context of usability.

We'll start with the calculation.

How to Calculate the SUS Score

One fault of the SUS score is how complicated it is to interpret. The odd-numbered questions and even-numbered questions get scored differently.

Let's walk through an example.

System Usability Scale Example

Customer A filled out questions 1-10 with the following rankings:

1. 4
2. 2
3. 5
4. 1
5. 3
6. 2
7. 4
8. 2
9. 5
10. 1

Step 1: Add up the total for the odd-numbered questions (1, 3, 5, 7, 9). Then, subtract 5 from the total to get your odd score.

• Odd score = (4+5+3+4+5) = 21 - 5 = 16. Your odd score is 16.

Step 2: Add up the total score for the even-numbered questions (2, 4, 6, 8, 10). Then, subtract the total from 25 to get your even score.

• Even score = (2+1+2+2+1) = 25 - 8 = 17. Your even score is 17.

Step 3: Add up your odd score and even score. Then multiply the sum by 2.5. This is your final SUS score out of 100.

• 16 + 17 = 33 x 2.5 = 82.5. Your final SUS score is 82.5.

But what does this score even mean? Let's look at it in context.

Interpreting Your Score

According to Usability.gov, a SUS score above a 68 is considered average, and anything below is considered below average. You could also group the number of scores you receive to determine what percentage of respondents gave you a high or low score.

The image below gives you a better snapshot of the range of scores and what they mean. In general:

• Scores below 50 are considered 'Not Acceptable'
• Scores between 51-70 are considered 'Marginal'
• Scores above 71 are considered 'Acceptable'

Now, let's get into the benefits of using the SUS.

Benefits of Using the System Usability Scale

1. It provides an at-a-glance snapshot of how usable or unusable your system is.

By looking at a single number, anyone can understand how users feel about the usability of whatever you're evaluating.

2. It's easy to use, at scale or with a small number of respondents.

SUS surveys can be administered in-person, via email, or across a variety of other media to get the answers needed to evaluate the score.

3. It can be repeated for many different products and systems.

You can use the SUS over and over again for different products and still achieve reliable results. Plus, you can also use it as a tool to compare the usability of one product or system to another.

However, no user testing method is perfect. Even with the benefits, there are some shortcomings to consider. Jakob Nielsen, co-founder of Nielsen Norman Group, offers an interesting take on the usefulness of the System Usability Scale in the video below.

Either way, the good news is that you don't have to recreate the wheel if you're interested in running a System Usability Scale survey. The template below makes it easier than ever to execute.

System Usability Scale Template

The below SUS template from Measuring X allows you to apply the System Usability Survey based on your specific needs.

Image source

The System Usability Scale can be a great way to determine how efficient, intuitive, easy, and satisfactory your product is in the eyes of your customer. And that customer feedback is extremely valuable in helping you improve the user experience.

Editor's note: This post was originally published in November 2018 and has been updated for comprehensiveness.