System Usability Scale: 10 Powerful Insights You Need Now

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Ever wondered how to measure if your users actually *like* using your product? Enter the System Usability Scale (SUS) — a simple, powerful tool that turns user frustration into actionable data. Let’s dive into why it’s a game-changer.

Table of Contents

What Is the System Usability Scale (SUS)?

The System Usability Scale, commonly known as SUS, is a 10-item questionnaire designed to evaluate the perceived usability of a system, product, or service. Developed in the late 1980s by John Brooke at Digital Equipment Corporation, SUS has since become one of the most widely used tools in usability assessment across industries — from software and websites to medical devices and consumer electronics.

What makes SUS stand out is its simplicity and reliability. Despite having only ten questions, it delivers a robust quantitative score that reflects how usable users find a system. The questionnaire is technology-agnostic, meaning it can be applied to virtually any interactive system, regardless of platform or complexity.

Origins and Development of SUS

The System Usability Scale was first introduced in 1986 during usability research at Digital Equipment Corporation. At the time, there was a growing need for a standardized, lightweight method to compare the usability of different systems without requiring extensive user testing or complex metrics.

John Brooke’s goal was to create a tool that was quick to administer, easy to analyze, and could be used across diverse technologies. The result was a ten-question Likert-scale survey that could be completed in under 10 minutes. Since its inception, SUS has been validated through numerous studies and is now considered a gold standard in usability measurement.

One of the key reasons for its longevity is its adaptability. Unlike other usability tools that require specific contexts or training, SUS can be used by designers, developers, product managers, and researchers alike. Its widespread adoption has led to the creation of benchmark scores, allowing teams to compare their product’s usability against industry standards.

How SUS Differs From Other Usability Metrics

While there are many tools to assess usability — such as the Nielsen Norman Group’s usability testing methods or the Task Success Rate — SUS stands apart because it measures *perceived* usability rather than performance-based metrics.

For example, task success rate tells you whether users completed a task, but not how easy or frustrating it was. SUS, on the other hand, captures the user’s subjective experience — their feelings about ease of use, consistency, and learning curve.

Performance Metrics: Measure what users *do* (e.g., time on task, error rate).
Perception Metrics: Measure what users *think* (e.g., SUS, UMUX, SUPR-Q).
SUS blends both: While it’s perception-based, its scoring correlates strongly with actual usability performance.

This dual nature makes SUS incredibly valuable. It’s not just about whether users succeed — it’s about whether they *feel* successful.

“The System Usability Scale is not the best usability scale because it’s perfect — it’s the best because it’s practical, reliable, and universally applicable.” — Jakob Nielsen, Nielsen Norman Group

How the System Usability Scale Works

The brilliance of the System Usability Scale lies in its simplicity. It consists of ten statements, each rated on a five-point Likert scale ranging from “Strongly Disagree” to “Strongly Agree.” The statements alternate between positive and negative polarity to reduce response bias.

After users complete a task or interaction with a system, they’re asked to respond to the following ten items:

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 system 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.Notice how odd-numbered items are positively worded, while even-numbered ones are negatively worded..

This design helps prevent users from mechanically agreeing or disagreeing with all statements..

Scoring the System Usability Scale

Scoring SUS is straightforward but requires careful attention to the alternating polarity of the questions. Here’s the step-by-step process:

For **odd-numbered items** (positive), subtract 1 from the user’s response (which ranges from 1 to 5). So, a response of 5 becomes 4, 4 becomes 3, etc.
For **even-numbered items** (negative), subtract the user’s response from 5. So, a response of 1 becomes 4, 2 becomes 3, etc.
Sum all the converted scores (now on a 0–4 scale).
Multiply the total by 2.5 to convert it to a 0–100 scale.

The final score ranges from 0 to 100, with higher scores indicating better perceived usability. A score of 68 is considered average, based on extensive benchmarking studies.

For example, if a user’s adjusted total before multiplication is 27, the SUS score is 27 × 2.5 = 67.5 — just below average.

This scoring method may seem quirky, but it ensures that both positive and negative responses contribute equally to the final score. The multiplication by 2.5 normalizes the score to a more intuitive 0–100 range, making it easier to communicate results to stakeholders.

Interpreting SUS Scores: What Do They Mean?

Understanding what a SUS score means in practical terms is crucial. While the score is numerical, its interpretation is qualitative. Here’s a widely accepted grading scale:

90–100: Excellent (Best in class, rare)
80–89: Good (Above average, desirable)
70–79: Acceptable (Average to slightly above)
60–69: Poor (Below average, needs improvement)
50–59: Awful (Unacceptable for most products)
0–49: Unacceptable (Critical usability issues)

According to research by Sauro and Bangor (2009), only about 10% of systems score above 85. A score above 80 is considered “good,” while anything below 70 should raise red flags.

It’s also important to consider the context. A mobile banking app scoring 65 might be unacceptable due to high user expectations, while a specialized industrial control system with the same score might be considered reasonable given its complexity.

Another key insight: SUS scores can be used to track usability improvements over time. For instance, if a redesign increases the SUS score from 62 to 78, that’s a significant usability win — even if users still report minor issues.

“A SUS score is not just a number — it’s a snapshot of your user’s experience. It tells you whether your design is helping or hindering them.” — Dr. James Lewis, IBM Human Factors Researcher

Why the System Usability Scale Is So Widely Used

The System Usability Scale has achieved near-universal adoption in UX research, product development, and academic studies. But what makes it so enduringly popular? The answer lies in its unique combination of reliability, simplicity, and flexibility.

Unlike more complex usability frameworks that require extensive training or software, SUS can be administered by anyone with basic research skills. It doesn’t require video recording, eye-tracking, or specialized labs. All you need is a way to present the ten questions and collect responses — which can be done via paper, email, or online survey tools.

Reliability and Validity of SUS

One of the most cited reasons for SUS’s popularity is its strong psychometric properties. Numerous studies have confirmed that SUS is both reliable (consistent across repeated measurements) and valid (it actually measures what it claims to measure — usability).

A 2009 study by Jim Sauro analyzed over 2,000 SUS scores and found that the internal consistency (Cronbach’s alpha) was typically above 0.9, which is considered excellent in survey research. This means the ten items are measuring the same underlying construct — perceived usability — rather than random opinions.

Furthermore, SUS scores correlate strongly with other usability metrics, such as task completion rates and user satisfaction. This predictive validity makes SUS more than just a “feel-good” metric — it’s a practical indicator of real-world performance.

For example, a product with a SUS score below 50 is likely to have high user abandonment rates, while one scoring above 80 is more likely to see high adoption and retention.

Flexibility Across Platforms and Industries

Another reason for SUS’s widespread use is its platform independence. Whether you’re testing a mobile app, a desktop software suite, a kiosk interface, or a smart home device, SUS can be applied without modification.

This universality makes it ideal for cross-product comparisons. For instance, a company might use SUS to compare the usability of its old and new website, or to benchmark its product against competitors.

Industries that rely heavily on SUS include:

Healthcare: Evaluating medical devices and electronic health records (EHRs).
Finance: Testing online banking platforms and investment apps.
E-commerce: Measuring checkout flow usability.
Education: Assessing learning management systems (LMS).
Government: Improving citizen-facing digital services.

The U.S. Department of Veterans Affairs, for example, uses SUS to evaluate the usability of its digital health tools, ensuring veterans can access care without technological barriers.

Step-by-Step Guide to Administering the System Usability Scale

Using the System Usability Scale effectively requires more than just handing out a questionnaire. To get meaningful results, you need to follow a structured process — from planning to analysis.

Here’s a comprehensive guide to administering SUS in your next usability study.

When and How to Deploy SUS

The best time to administer SUS is immediately after a user completes a set of representative tasks with your system. This ensures their experience is fresh and contextually relevant.

For example, if you’re testing an e-commerce app, ask users to:

Search for a product
Add it to the cart
Proceed to checkout
Complete a mock purchase

Right after this sequence, present the SUS questionnaire. This timing captures their holistic impression of the interaction, not just isolated moments.

You can deploy SUS in various formats:

In-person testing: Hand a printed form or display it on a tablet.
Remote moderated sessions: Share the survey via screen sharing.
Unmoderated remote testing: Embed SUS in tools like UsabilityHub or UserZoom.
Email surveys: Send it to users after they’ve used your product in real-world conditions.

Each method has trade-offs. In-person gives richer context, while remote scales better. Choose based on your goals and resources.

Best Practices for Accurate Results

To ensure your SUS data is reliable, follow these best practices:

Use a representative sample: Aim for at least 15–20 users for stable results.While SUS can be used with as few as 5 users, larger samples reduce variability.Randomize task order: If testing multiple systems, randomize the order to avoid learning or fatigue effects.Don’t influence responses: Avoid leading questions or body language that might bias answers.Collect qualitative feedback: Pair SUS with open-ended questions like “What did you find most confusing?” to enrich interpretation.Normalize scoring: Always use the standard scoring method — don’t invent your own formula.One common mistake is administering SUS too early — for example, after only one simple task..

This can skew results because users haven’t experienced the full system.Always ensure they’ve interacted meaningfully before asking for feedback..

“The SUS is only as good as the context in which it’s used. Administer it at the right time, with the right users, and you’ll get gold-standard insights.” — Dr. Jeff Sauro, MeasuringU

Interpreting and Acting on SUS Results

Getting a SUS score is just the beginning. The real value comes from interpreting the data and turning it into action. A number alone won’t improve your product — but insights will.

Let’s explore how to make sense of your results and drive meaningful change.

Comparing Scores to Benchmarks

One of the most powerful uses of the System Usability Scale is benchmarking. By comparing your score to industry averages, you can gauge how your product stacks up.

According to Sauro’s research, the average SUS score across thousands of studies is 68. Here are some typical benchmarks by industry:

Consumer Software: 75–80
Enterprise Software: 65–70
Mobile Apps: 70–78
Medical Devices: 60–65
Government Websites: 60–68

If your mobile app scores 62, that’s below average — a clear signal for improvement. If your internal HR tool scores 72, that’s actually good for enterprise software.

You can also conduct competitive benchmarking. Test your product against key competitors using the same tasks and SUS administration. A higher SUS score can become a selling point — “Our app is 20% more usable than the leading alternative.”

Identifying Usability Weaknesses from SUS Items

While the overall SUS score is useful, don’t ignore the individual item responses. They can reveal specific pain points.

For example, if users strongly disagree with “I found the system unnecessarily complex” (Item 2), that’s good — the system feels simple. But if they agree with “I think I would need technical support to use this system” (Item 4), that’s a red flag.

Here’s how to analyze item-level data:

Calculate average responses for each item.
Identify items with low scores (e.g., average below 2.5 on the 1–5 scale).
Group items by theme: learning curve, consistency, confidence, complexity.
Triangulate with qualitative feedback to understand the “why” behind low scores.

Suppose Item 8 (“I found the system very cumbersome to use”) scores poorly. This suggests workflow inefficiencies. Combine this with session recordings to see where users hesitate or backtrack.

Similarly, low scores on Item 10 (“I needed to learn a lot before getting going”) indicate poor onboarding. This could lead to a redesign of the first-time user experience.

Advanced Applications of the System Usability Scale

While SUS is often used in basic usability testing, its applications go far beyond. Advanced teams leverage SUS for strategic decision-making, longitudinal tracking, and even predictive analytics.

Let’s explore some of these sophisticated uses.

Using SUS for Product Iteration and Redesign

One of the most impactful uses of SUS is tracking usability over time. By measuring SUS before and after a redesign, you can quantify the impact of your changes.

For example, a fintech startup might:

Run a baseline SUS test on their current app (score: 64).
Redesign the onboarding flow and navigation.
Re-test with a new group of users (score: 79).
Conclude that the redesign improved perceived usability by 15 points — a significant gain.

This data can justify design decisions to stakeholders, secure funding for UX improvements, or guide future iterations.

Some teams even use SUS as a KPI in agile sprints. If a sprint’s goal is to improve usability, a post-sprint SUS test can validate success.

SUS in Academic and Clinical Research

The System Usability Scale is not just for product teams — it’s a staple in academic research. Thousands of peer-reviewed studies cite SUS as a primary usability metric.

In healthcare, SUS is used to evaluate:

Patient portals
Telehealth platforms
Wearable medical devices
Clinician-facing software

A 2020 study published in the Journal of Medical Internet Research used SUS to compare two diabetes management apps, finding a 12-point difference in usability that correlated with patient adherence rates.

In clinical settings, a high SUS score can mean the difference between a device being adopted or abandoned by healthcare providers. Given the high stakes, SUS provides a low-cost, high-value way to ensure usability.

“In medical device design, usability isn’t a luxury — it’s a safety requirement. SUS helps us ensure that clinicians can use our tools correctly, especially under stress.” — Dr. Beth Crandall, Cognitive Scientist

Common Misconceptions and Limitations of SUS

Despite its strengths, the System Usability Scale is not a magic bullet. It has limitations, and misunderstanding them can lead to poor decisions.

Let’s clear up some common myths and address its constraints.

What SUS Does NOT Measure

It’s crucial to understand what falls outside SUS’s scope:

Emotional engagement: SUS doesn’t measure delight, frustration, or brand loyalty.
Accessibility: A system can score high on SUS but still be unusable for people with disabilities.
Performance metrics: SUS won’t tell you how long tasks take or how many errors occur.
Specific design flaws: It identifies *that* there’s a problem, but not *where* or *how* to fix it.

For example, a user might find a system easy to use (high SUS) but still make critical errors due to poor feedback design. That’s why SUS should be part of a broader usability strategy, not the only tool.

Addressing Criticisms and Biases

Critics argue that SUS is too simplistic or prone to cultural bias. Some users may tend to agree with all statements (acquiescence bias), especially in cultures that value politeness.

To mitigate this:

Use neutral moderators.
Combine SUS with behavioral data.
Consider using the Adjusted SUS for specific populations.
Always pair SUS with qualitative interviews.

Another limitation is that SUS assumes users can self-report their experience accurately. Novice users might not recognize poor design, while experts might overlook complexity due to familiarity.

Therefore, SUS works best when used with a mix of user types — new, occasional, and experienced users — to get a balanced view.

Alternatives and Complements to the System Usability Scale

While SUS is powerful, it’s not the only usability metric available. Depending on your goals, you might want to use alternatives or combine SUS with other tools.

Combining SUS With Behavioral Data

The most powerful insights come from combining SUS with behavioral metrics:

Task Success Rate: Did users complete the task?
Time on Task: How long did it take?
Error Rate: How many mistakes were made?
Click Path Analysis: Where did users go off-track?

For instance, a user might report high confidence (SUS Item 9) but make repeated errors — indicating overconfidence or misleading feedback design.

By triangulating SUS with behavioral data, you get both the “what” and the “why” of usability.

What is the ideal sample size for SUS?

A minimum of 15–20 users is recommended for reliable results. While SUS can be used with as few as 5 users (especially in formative testing), larger samples provide more stable averages and allow for statistical comparisons.

Can SUS be used for non-digital products?

Yes! Although originally designed for software, SUS has been successfully applied to physical products like medical devices, ATMs, and even household appliances. The key is that the product must involve interactive use.

Is the System Usability Scale free to use?

Yes, the System Usability Scale is in the public domain and free for both commercial and academic use. No permission is required, though proper citation is appreciated.

How often should I run SUS tests?

Run SUS whenever you make significant changes to the user interface or user flow. Many teams use it at the end of each design sprint or major release. For continuous improvement, quarterly testing can track long-term trends.

Can SUS predict user retention?

Indirectly, yes. While SUS doesn’t measure retention directly, high usability is strongly correlated with user satisfaction and continued use. Products with SUS scores above 80 tend to have higher engagement and lower churn.

The System Usability Scale remains one of the most effective, efficient, and accessible tools for measuring perceived usability. Its simplicity belies its power — a single 10-item survey can reveal deep insights into how users experience your product. While it has limitations and should be used alongside other methods, SUS provides a standardized, reliable metric that teams can use to benchmark, compare, and improve. Whether you’re a startup founder, UX designer, or researcher, mastering SUS is a crucial step toward building more usable, user-friendly systems.