System Usability Scale (SUS)

It’s almost impossible to look into the System Usability Scale (SUS) without seeing it described as “quick and dirty.” The test was first designed by usability specialist John Brooke in 1986 for the British tech company Digital Equipment Corporation. The test’s ease of use and reliability made it wildly popular, such that Brooke even described it as “quick and dirty” in a 1995 academic paper, which further expanded the scale’s application. 

Why are people so drawn to the test? In short, the System Usability Scale provides a remarkably reliable benchmark to gauge how users feel about a particular system. Because it’s broad and simple, it can be used to test everything from hardware to software to mechanical operations in industries as varied as finance, automative design, and healthcare. If you’ve designed a system and want data about how your users feel about it, it’s a great option.

But, like any other tool, it benefits from a little context. Read on to learn more about how to employ and interpret the System Usability Scale to get the most out of it. 

If you're curious to find out what your SUS score is, we've created a System Usability Scale template that you can use to measure your product's usability.

What is the System Usability Scale (SUS)?

The System Usability Scale asks users to agree or disagree with a series of 10 statements about a system’s complexity, ease of use, enjoyability, and consistency. Users respond to each statement on a Likert scale of one (strongly disagree) to five (strongly agree). The statements alternate between gauging positive and negative sentiment, which means survey respondents can’t simply choose one response consistently down the entire survey.

The statements that make up the System Usability Scale are: 

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.

Pros and cons of the System Usability Scale

Over the course of decades, this simple, well-designed system has been used in countless contexts and translated into many languages. Paradoxically, the popularity of the scale is part of what continues to make it so popular. Professionals across disciplines and industries are familiar with it; its utility is well-documented and it provides a sturdy benchmark when compared to other systems, whether they’re being tested by your team or used by others in your industry.

Some of the key benefits of the SUS include: 

• It centers users: Each question centers on the user’s subjective interpretation of their experience. For teams interested in learning more about how users feel about a website, piece of software, or application, it’s very focused. 

• It provides solid quantitative data: The SUS outputs raw numbers that can be further filtered by personas and other subject types. It lends itself well to graphs, tables, and data-driven decision-making. 

• It’s quick and easy to deploy: Ten questions asked without a moderator is a much quicker way to gauge the usability of a given design than detailed user interviews or custom scales. This makes it useful for iterative designs, where slight moderations in a given system can be evaluated by ongoing implementation of the SUS. 

• It’s a great benchmark: The SUS has been tested many times over decades and across many industries. Assuming you deployed the test appropriately and tabulated the scores correctly, the numbers you receive can be applied to those of other tests so you know how your system measures up fairly objectively. 

• It’s reliable: You can trust the data coming out of the SUS. One study applied an eleventh question, which asked 1,000 users to apply an adjective to describe their experience with the given system. The study found a high correlation between the adjectival answer and the raw numeric answer determined by the SUS. 

A few considerations to keep in mind about the SUS are: 

• It’s not diagnostic: If your system is great, the SUS won’t tell you why people think it’s great. If your system needs improvements, the SUS won’t tell you what parts of it need work, either. You’ll need to complement the SUS with additional usability testing, either in concert with the SUS or afterward to figure that out. 

• Scoring can be complex: While getting responses from users is simple enough, scoring and interpreting the SUS is a little more complicated.

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How to use the SUS

The System Usability Scale is renowned for its applicability and ease of use. Let’s run through the steps to make sure you’re getting the most out of the scale, whether it’s your first or hundredth time using it. 

1. Deploy the SUS after a meaningful interaction 

The SUS is only useful if it measures a user’s feelings about your website, software, or tool after they’ve used it in a meaningful way. This could be at the end of a usability test in which they’ve performed multiple tasks. Or it could be distributed automatically to users who have performed a series of steps, like searching for a product, adding it to a cart, and successfully checking out. Either way, make sure users have‌ used your system before they’re invited to weigh in on it. 

2. Calculate your score 

Once you’ve collected a statistically significant amount of responses, you can calculate your score. 

• For each of the odd-numbered questions (1, 3, 5, 7, 9), subtract 1 from the score.

  • [User Rating] – 1 = ___ points

• For each of the even-numbered questions (2, 4, 6, 8, 10), subtract their value from 5.

  • 5 – [User Rating] = ___ points

• Add up the new values and multiply this by 2.5 to get an individual user’s score.

The resulting number will be between 0 and 100. This is the respondent’s score for your system on the SUS. Respondents’ scores can be averaged ‌together, or sliced more narrowly between demographics or personas to draw further inferences. 

If you're using Lyssna's SUS score calculation template, there's no need to do any manual calculations. Simply download your results as a CSV, make a copy of our Google Sheet template, and import your data. The SUS scores will automatically be calculated for you!

3. Interpret your score 

Now that you’ve got your score, there are a couple of ways you can evaluate it. 

Approval threshold

The average SUS score is 68. One way to use the scale is to set an acceptable threshold for your use case. Perhaps your team is focused merely on getting a system up and running; in this instance, the acceptable threshold might be 68 or above.

Alternately, maybe you’ve performed extensive testing and know that scores above 80 retain your key users. In this case, you may want to set your threshold higher. 

Percentile

If you don’t have a benchmark for an approval threshold, you can use your SUS score to determine what percentile your system performs better than. According to NNgroup, aggregate SUS score testing percentiles are as follows.

Keep in mind that percentiles tell you how well you performed against others. So if you scored a 74.1, your SUS score is higher (better) than 70% of other systems scored using the SUS over time. If you score 84.1, you did better than 96% of other systems that have undergone this test. 

Best practices for using SUS

You get it at this point: the SUS is a quick, time-tested way to obtain quantitative data about how users feel about your website, software, app, or other system. Here are a couple of final pointers on this handy benchmark: 

• If you’re using the SUS alongside a usability test, make sure participants complete at least one task. This ensures that they’re able to evaluate your product more broadly. 

• Combine your SUS scores with performance-based metrics, such as completion rates and task times. This guarantees that you’re not only collecting data about how users feel about the system but also how well it works outside of their subjective interpretation. 

• The SUS works well alongside other testing methods. It fits in well alongside usability testing, as mentioned above, but it also works well as part of an A/B test, in which two sets of users receive an identical experience with one variable changed. If the resulting SUS score of one group is statistically different than the other, you have actionable data about the impact of that variable on the overall system. 

• The SUS works well with iterative designs. For example, the A/B test mentioned above can help evaluate the efficacy of small iterations in user interfaces or workflows over time. 

• Use a template. The SUS is quick and cheap, but tabulating it can require a little bit of number-crunching. A template streamlines this and makes the SUS even easier to use.

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