How to use and implement the system usability scale (SUS)

Sure, aesthetics matter. A sleek interface and a carefully curated color palette grab attention and set the tone for a brand. When it comes to development, though, aesthetics is just one part of the equation. Usability is the true measure of success.

If your product looks great but nobody can use it, you’re headed for disaster. That means you need to ensure usability alongside aesthetics.

There are many ways to measure product usability, but the system usability score (SUS) is one of the most tried-and-true metrics. The tool helps you understand how effectively your product aligns with user needs and expectations. You can use it to measure usability for a website, app, or even a physical product. It’s incredibly simple to use, too. There are no bells or whistles, just a few questions and a formula to calculate your usability score.

Learn more about the SUS, what it is, why it matters, and how it can be used to create products that users will love.

The system usability scale measures how easy a product or system is to use. It’s a quick check-in on the user experience that can inform progress and improvements.

John Brooke first developed the SUS in the 1980s, and it has become a staple in the UX toolkit.

Incredibly, the SUS Brooke developed four decades ago hasn’t changed much in the modern age. The brilliance of the SUS is that it doesn’t get into specific usability issues. Instead, it gives a high-level overview of user satisfaction.

It’s a simple, easy-to-administer 10-item questionnaire. It asks users to rate their agreement with statements on a Likert scale from 1 (strongly disagree) to 5 (strongly agree).

The statements cover a range of usability aspects, from how easy the system is to use to how complex the user thinks the system is.

The 10 classic SUS questions are:

1. I think that I would use this system frequently.

2. I think the system is unnecessarily complex.

3. I think the system is easy to use.

4. I think I would need the support of a technical person to be able to use this system.

5. I think that the various functions in the system were well integrated.

6. I think there was too much inconsistency in the system.

7. I think that most people would learn to use this system very quickly.

8. I found the system cumbersome to use.

9. I felt very confident using the system.

10. I needed to learn a lot of things before I could start using this system.

One of the great things about the SUS is its adaptability. You can tweak these standard questions to fit your specific service or product. However, it’s recommended that you stick to the original wording, as these questions have been tested over time and found to be reliable usability indicators.

User experience is everything. No matter what you create, your users expect your product to be intuitive, efficient, and enjoyable to use. The SUS gives you high-level insight into how you are meeting those expectations (or not).

The SUS can give you the following:

• Quantifiable data: you can turn subjective user experiences into objective quantifiable data. It allows you to take a data-driven approach to deciding how and why you want to improve your product.

• Benchmarking: you can see how your SUS score measures up against industry benchmarks or previous product versions.

• Prioritization: use the SUS to pinpoint areas or features of the product that cause the most frustration or require the most UX improvement.

• Return on investment (ROI): improving usability increases user satisfaction, reduces support costs, and boosts conversions—all great ways to drive business growth.

The SUS helps you create products that people love to use. And really, isn’t that the goal of any business?

The SUS score ranges from 0 to 100, where 0 indicates the lowest perceived usability and 100 represents the highest.

The average SUS score across a wide range of industries and products is approximately 68. Scores above this threshold are generally considered above average, while scores below 68 suggest below-average usability.

Remember, these are just general guidelines. While these ranges can give you a general sense of how your product is performing, you’ll also want to consider your specific industry, target audience, and the complexity of your product.

For instance, a SUS score that is considered average in one industry might be seen as inadequate in another where we would expect higher usability standards. Therefore, while SUS scores are a useful starting point, you should contextualize them within specific domain and user expectations to draw more accurate conclusions about your product’s usability.

The SUS can be a valuable tool for measuring usability, but, like any method, it has strengths and weaknesses. You’ll want to know what they are before you use the scale to determine your product’s usability.

Pros

• Objective user feedback: the SUS provides a quantitative measure of user satisfaction, taking the guesswork out of understanding user experiences. It’s also a reliable way to compare the usability of different versions of your whole product or system over time.

• Wide applicability: the SUS is versatile enough to evaluate a wide range of products, from websites to software to physical items. It’s a simple tool accessible to teams with varying tech skills or UX expertise.

• Benchmarking and comparisons: comparing your SUS scores over time to industry benchmarks can reveal areas that need improving.

Cons

• Limited contextual information: while the SUS gives you an overall usability score, it doesn’t provide details about any specific issues your users might experience. This means you won’t learn what’s causing user frustration. You’ll need additional research methods for that.

• Interpretation challenges: the SUS gives you a numerical score, but it can be ambiguous. Factors like a product’s complexity and target audience can influence what’s considered “good.”

• Cultural and language biases: the SUS was developed in English, and translating the questionnaire into other languages can introduce cultural and language biases. To mitigate these issues, validate the translated versions to ensure they are culturally appropriate and accurately convey the intended meaning.

The SUS is relatively straightforward to administer—one reason it has become an industry staple over the last four decades. Here’s what you’ll need to do:

1. Understand the basics of the SUS

Start by getting to grips with the basics of the SUS concept, including its purpose and limitations. Then, review the questions on the SUS to ensure you know what they are measuring and why.

2. Define your study objectives

Outline what you want to achieve with a SUS evaluation. Are you comparing different versions of your product? Measuring user satisfaction with a new feature? Or are you doing your first SUS to establish a baseline?

3. Customize the SUS questionnaire

The standard SUS questions are effective, but there’s room to align them with your specific product or service. Try to maintain each question’s core structure and wording so that you get an accurate usability measurement.

4. Recruit participants

Identify your target user group and recruit people in this demographic, using screening questions to ensure participants are within your target user group.

Consider offering incentives to encourage participation. The more participants you have, the more statistically accurate your results will be.

For initial, formative testing, a smaller sample size of 5–10 participants may suffice. For more comprehensive evaluations or benchmarking, aim for a sample size of 20–30 or more to achieve greater precision and confidence in the findings.

Use our handy guide to find out how big your sample size should be.

5. Administer the SUS questionnaire

Once you have your participants, you can administer the SUS questionnaire. This can be done in person or online.

Make sure the participants complete the questionnaire after using your product or system.

6. Calculate and interpret SUS scores

Once you’ve collected your data, you’ll need to calculate the score for each participant. The standard formula is:

• Subtract 1 from the user’s response to odd-numbered questions (1, 3, 5, 7, 9). For example, Susan marks question #3 as a 5 (strongly agree): 5-1 = 4

• For the even-numbered questions (2, 4, 6, 8, 10), subtract the user’s response from 5. For example, Susan marks question #4 as a 3 (neither agree nor disagree): 5-3 = 2

Add up all the new scores and multiply them by 2.5. This will give you your SUS score out of a possible 100.

Remember, an SUS score isn’t given as a percentage.

Calculating your SUS score is just the beginning. You have a number, but what does it mean?

Here are five ways to interpret your score to make more sense of your data and turn it into actionable insights.

Assessing usability through grading

The most straightforward approach is to assign a letter grade to your SUS score. For example:

• A+: 90–100

• A: 80–89

• B: 70–79

• C: 60–69

• D: 50–59

• F: below 50

Comparative analysis with percentiles

You can also compare your SUS score to industry benchmarks or historical data.

Calculating percentiles lets you determine how your product stacks up against competitors or previous versions. For instance, a SUS score in the 90th percentile indicates that your product performs better than 90% of similar products.

Descriptive adjectives for usability

Assigning a description adjective to your SUS score ranges can make it easier for stakeholders to understand. For example, you might use a scale like this:

• Excellent: 85+

• Good: 75–84

• Average: 65–74

• Fair: 55–64

• Poor: below 55

Telling a stakeholder that your SUS score was excellent is clearer than simply telling them it was 86.

Categorizing usability acceptability

You can also define acceptable ranges for usability scores to help you make informed decisions. Bangor and colleagues (2008) introduced three levels of acceptability:

• Not acceptable (0–50)

• Marginal (50–70)

• Acceptable (above 70)

Remember to consider your industry’s averages. For example, a SUS score of 70 or higher might be positive in your industry, while anything under that indicates a need for improvement. Having an acceptability cutoff can give you a benchmark for evaluating your products.

Linking usability to recommendations

Understanding your SUS score can inform your design and development decisions, helping you create a product development roadmap.

For example, a low SUS score might prompt you to conduct usability testing, while a high score could help justify ongoing investment.

The SUS can be an excellent framework for assessing usability, but you can make it even more effective by doing the following:

• Combining it with qualitative data: the SUS is a snapshot of user satisfaction. It doesn’t tell you why users feel how they do. Combining your SUS data with qualitative research, such as user interviews, can give you deeper insight. You’ll understand why your score is what it is and where you can focus your improvement efforts.

• Using it to iterate and improve: your SUS score isn’t a one-time measurement. You should use it as a baseline to track changes over time. Conducting regular SUS studies will help you measure the impact of your decisions and identify trends. An iterative approach can help you continuously improve your project and usability scores.

• Involving stakeholders: don’t gatekeep your SUS scores. Share them with people across your team, from designers to developers, managers, and stakeholders. Sharing the results helps you create a culture of continuous improvement and gives everyone insight into the user’s needs.

The SUS is a staple measurement for a reason—it works. But it’s also not the only research method out there, nor is it the only one your team should use. You can complement it with other research methods, such as:

• Heuristic evaluation: a heuristic evaluation involves allowing usability experts to examine and evaluate your product or system against established usability principles. They can help you identify potential issues without involving users in the process.

• Usability testing: usability testing involves one-on-one interviews with users to observe how they complete tasks with your product. Ask them to think out loud to learn about their mental process, experiences, and needs.

• Task success rate: measure the percentage of users who can successfully complete specific tasks within your product. This quantitative metric provides insights into usability and performance by indicating how effectively users can achieve their goals without encountering issues.

• A/B testing: experiment with different design variations and determine which performs better. This method can help you optimize specific features of your product or service based on user behavior.

• Analytics and usage data: analyze user behavior data to identify patterns, drop-off points, and areas where users struggle or excel, providing a broader context to SUS findings.

The system usability scale can help you determine the usability of your product or service. But don’t use it in isolation. Combine the SUS with other research methods and share those results far and wide. You’ll gain a deeper understanding of what your users want and need and be able to improve your product or system continuously. You’ll end up with something successful that your customers love to use, come back to repeatedly, and recommend to others.

Measuring SUS over time can help you create exceptional user experiences and write a recipe for business growth.