System Usability Scale

System Usability Scale (SUS) is a quick, standardized questionnaire that measures the perceived usability of a product or system. It provides researchers and designers with a reliable score that indicates how usable and satisfying users find an interface, helping teams identify areas for improvement.

What is the System Usability Scale?

The System Usability Scale (commonly abbreviated as SUS) is a ten-question survey developed by John Brooke in 1986 while working at Digital Equipment Corporation. Despite its age, SUS remains one of the most widely used usability questionnaires in UX research because it's:

• Quick to administer: Takes just 2-3 minutes for users to complete
• Technology-agnostic: Works for websites, apps, hardware, and virtually any interactive system
• Validated: Backed by extensive research proving its reliability
• Easy to score: Produces a single, comparable score on a scale of 0-100

SUS has become the industry standard for measuring perceived usability, giving teams a quantifiable way to evaluate and improve user experience.

Why SUS Matters

Implementing the System Usability Scale offers several key benefits:

• Benchmark data: SUS provides a score that can be compared against industry averages or your own previous iterations
• Problem detection: Helps identify usability issues that might otherwise be missed
• Resource efficiency: Delivers meaningful insights with minimal time investment
• Stakeholder communication: Offers a single, easy-to-understand number for demonstrating progress to non-UX team members
• Competitive analysis: Allows comparison of your product against competitors

Most importantly, SUS helps teams measure what matters—the actual user experience—rather than relying solely on assumptions or engagement metrics that don't necessarily reflect usability.

How SUS Works

The System Usability Scale consists of 10 alternating positive and negative statements that users rate on a 5-point scale from "Strongly Disagree" to "Strongly Agree." The statements cover various aspects of usability, including:

1. Frequency of system use
2. System complexity
3. Ease of use
4. Need for technical support
5. Feature integration
6. Inconsistency
7. Learnability
8. Cumbersomeness
9. Confidence in using the system
10. Learning curve

The SUS Questions

Here are the exact 10 statements users respond to:

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.

Calculating SUS Scores

The scoring process involves:

1. For odd-numbered questions (positive statements), subtract 1 from the user's response
2. For even-numbered questions (negative statements), subtract the user's response from 5
3. This converts all values to a scale from 0 to 4, with 4 being the most positive response
4. Add up these converted responses and multiply by 2.5
5. This gives you a SUS score from 0 to 100

A score of 68 is considered average. Scores above 80 are excellent, while scores below 50 indicate serious usability problems.

Best Practices for Using SUS

✅ Administer at the right time: Use SUS after participants have had enough interaction with the system to form an opinion, but before a detailed debriefing

✅ Collect qualitative data too: Pair SUS with open-ended questions or interviews to understand the "why" behind the scores

✅ Use consistent timing: For comparative studies, administer SUS at the same point in the user journey

✅ Maintain original wording: Don't modify the questions, as this can affect the reliability of the score

✅ Sample appropriately: Aim for at least 5-8 participants per user group for meaningful results

✅ Set benchmarks: Establish your own baseline scores to track improvements over time

Common SUS Mistakes to Avoid

❌ Relying solely on the overall score: Look for patterns in individual question responses for deeper insights

❌ Testing with the wrong users: Make sure participants represent your actual target audience

❌ Administering too early: Don't use SUS before users have had meaningful interaction with the system

❌ Comparing across different types of systems: A score for a mobile app isn't directly comparable to a score for a complex enterprise system

❌ Treating SUS as comprehensive: Remember that SUS measures perceived usability, not actual performance or other aspects of UX

❌ Modifying the questions: Changing the wording invalidates the standardized nature of the test

Connecting SUS with Card Sorting

Card sorting and SUS complement each other well in a comprehensive UX research strategy:

• Use card sorting early in the design process to develop an intuitive information architecture
• Apply SUS later to validate whether the implemented design is actually perceived as usable

For example, if you receive a low SUS score related to system complexity or feature integration (questions 2 and 5), this might indicate information architecture issues. In this case, you could use card sorting to better understand users' mental models and reorganize your navigation or content structure.

Card sorting helps you build intuitive structures, while SUS helps you measure if those structures actually create a usable experience—making them powerful partners in your UX toolkit.

Get Started with SUS

Ready to implement the System Usability Scale in your research? Begin by establishing a baseline score for your current product, then use it to track improvements over time. Combine SUS with other research methods like card sorting to get a holistic view of your user experience and identify specific areas for enhancement.