If you’ve ever wondered how users truly feel about a product’s ease of use, the System Usability Scale (SUS) is your go-to tool. Simple, reliable, and widely trusted, it turns subjective opinions into actionable data—fast.
What Is the System Usability Scale (SUS)?
The System Usability Scale, commonly known as SUS, is a 10-item questionnaire designed to measure the perceived usability of a system, product, or service. Developed in 1986 by John Brooke at Digital Equipment Corporation, SUS has since become one of the most widely used tools in usability evaluation across industries—from software and websites to medical devices and consumer electronics.
Origins and Development of SUS
John Brooke created the SUS during a time when usability testing was gaining momentum but lacked a standardized, lightweight metric. He aimed to design a tool that was quick to administer, easy to score, and applicable across different types of systems, regardless of their complexity or domain.
The original research was conducted to support internal usability assessments within a corporate environment, but its simplicity and reliability led to widespread adoption beyond its initial scope. Over the decades, SUS has been validated through numerous studies and is now considered a gold standard in usability measurement.
One of the key strengths of the SUS is that it doesn’t require users to have technical knowledge. It focuses on the user’s subjective experience—how easy or difficult they found the system to use—making it accessible and effective across diverse user groups.
Structure of the 10-Item Questionnaire
The SUS consists of 10 statements, each rated on a 5-point Likert scale ranging from “Strongly Disagree” (1) to “Strongly Agree” (5). The statements alternate between positive and negative phrasing to reduce response bias. For example:
- I think that I would like to use this system frequently. (Positive)
- I found the system unnecessarily complex. (Negative)
- I thought the system was easy to use. (Positive)
- I think that I would need the support of a technical person to be able to use this system. (Negative)
After users complete the survey, each item is scored based on whether it’s positively or negatively worded. The scoring algorithm adjusts for reverse scoring on odd-numbered items (which are negatively phrased), and the final score is calculated on a scale from 0 to 100.
“The beauty of the SUS lies in its simplicity. It doesn’t tell you *why* a system is usable, but it gives you a reliable number that tells you *how* usable it is.” — Jeff Sauro, MeasuringU
Why SUS Stands Out Among Usability Metrics
Unlike more complex usability frameworks that require extensive observation, task analysis, or eye-tracking, the SUS is fast, cost-effective, and scalable. It can be administered after a usability test, embedded in a post-task survey, or sent out remotely to a large user base.
Its versatility allows it to be used in both formative and summative evaluations. In early design phases, SUS helps identify major usability issues. In later stages, it provides a benchmark for comparing different versions of a product or competing systems.
Moreover, because SUS produces a single numerical score, it’s easy to communicate findings to stakeholders, developers, and non-technical team members. This makes it an invaluable tool for bridging the gap between user experience research and business decision-making.
How to Administer the System Usability Scale
Administering the System Usability Scale correctly is crucial to obtaining reliable and valid results. While the process is straightforward, attention to timing, context, and user selection can significantly impact the quality of the data collected.
When to Use SUS in the Design Process
The SUS can be used at various stages of product development. In the early stages (formative evaluation), it helps identify usability pain points during prototype testing. For example, after users complete a series of tasks on a wireframe or beta version, administering the SUS provides quick feedback on overall usability.
In later stages (summative evaluation), the SUS serves as a benchmarking tool. Teams can compare SUS scores across different versions of a product to measure improvement. It’s also commonly used in competitive analysis—testing your product against a competitor’s to see which performs better in perceived usability.
Best practice suggests using SUS after users have completed a realistic set of tasks. This ensures that their responses are based on actual interaction rather than first impressions or superficial exploration.
Best Practices for Survey Distribution
To get the most accurate results, the SUS should be administered in a way that minimizes bias and maximizes response quality. Here are some recommended practices:
- Use digital survey tools: Platforms like Google Forms, SurveyMonkey, or Typeform make it easy to distribute and collect SUS responses efficiently.
- Keep it anonymous: Allowing users to respond anonymously encourages honesty, especially if they had a negative experience.
- Time it right: Administer the SUS immediately after the usability session while the experience is still fresh in the user’s mind.
- Provide clear instructions: Explain that there are no right or wrong answers and that you’re interested in their honest opinion.
For remote usability testing, tools like MeasuringU offer validated SUS templates and automated scoring, making the process even smoother.
Avoiding Common Administration Mistakes
Despite its simplicity, several pitfalls can compromise the validity of SUS results:
- Administering SUS without task completion: Giving the survey before users have interacted meaningfully with the system leads to unreliable data.
- Using it in isolation: While SUS gives a great overall score, it doesn’t explain *why* users felt a certain way. Always pair it with qualitative feedback like interviews or think-aloud protocols.
- Modifying the wording: Even small changes to the SUS questions can invalidate the scoring model. Stick to the original wording to ensure comparability with established benchmarks.
- Ignoring sample size: While SUS can technically be used with small samples (as few as 5 users), larger samples (20+) provide more stable and generalizable results.
By avoiding these common errors, teams can ensure that their SUS data is both accurate and actionable.
Scoring and Interpreting the System Usability Scale
One of the most appealing aspects of the System Usability Scale is its straightforward scoring method. Despite its simplicity, the scoring system is mathematically sound and produces a reliable usability score that can be compared across studies and industries.
Step-by-Step Scoring Methodology
Scoring the SUS involves a few simple steps:
- For each of the 10 items, subtract 1 from the user’s response (so responses range from 0 to 4).
- For odd-numbered items (1, 3, 5, 7, 9), which are positively worded, use the adjusted score as-is.
- For even-numbered items (2, 4, 6, 8, 10), which are negatively worded, reverse the score by subtracting it from 4.
- Sum all 10 adjusted scores and multiply the total by 2.5 to convert it to a 0–100 scale.
For example, if a user responds with all 3s (neutral), the raw sum would be 20 (5 items × 2 + 5 items × 2), multiplied by 2.5 gives a final SUS score of 50—right at the average benchmark.
This method ensures that higher scores always indicate better perceived usability, regardless of question phrasing.
Understanding SUS Score Benchmarks
Once you have a SUS score, the next step is interpreting it. Over the years, researchers have established useful benchmarks:
- Below 50: Poor usability. Users likely struggled significantly.
- 50–69: Average. Room for improvement.
- 70–79: Good. Meets expectations for most systems.
- 80–89: Excellent. Top-tier usability.
- 90–100: Outstanding. Rare and exceptional.
According to research by Sauro and Lewis (2006), the average SUS score across thousands of studies is around 68. This means a score above 70 is already better than average.
It’s also helpful to compare your score against industry-specific benchmarks. For example, consumer apps often score higher than enterprise software due to greater investment in UX design.
“A SUS score of 70 doesn’t mean your product is ‘good enough’—it means it’s average. In competitive markets, average isn’t acceptable.” — Jakob Nielsen, Nielsen Norman Group
Comparing SUS Scores Across Products
One of the most powerful uses of SUS is comparative testing. By administering the same survey to users interacting with two different systems, you can determine which one is perceived as more usable.
For instance, a company might test Version A and Version B of a mobile app. If Version A scores 65 and Version B scores 82, the improvement is not only statistically significant but also practically meaningful.
Statistical tests like the paired t-test can be used to determine if the difference between two SUS scores is significant. Tools like MeasuringU’s SUS Calculator automate this process and provide confidence intervals, making interpretation easier.
However, remember that SUS measures *perceived* usability, not objective performance. A system might be fast and efficient but still receive a low SUS score if users *feel* it’s complicated. That’s why combining SUS with behavioral metrics (like task success rate or time on task) gives a more complete picture.
Advantages of Using the System Usability Scale
The System Usability Scale has stood the test of time for good reason. Its widespread adoption is not due to marketing hype but to real, measurable benefits that make it indispensable in usability research.
Reliability and Validity of SUS
One of the most cited advantages of the SUS is its strong psychometric properties. Numerous studies have confirmed its reliability (consistency of results) and validity (accuracy in measuring what it claims to measure).
Research shows that SUS has high internal consistency, with Cronbach’s alpha typically above 0.9, indicating that the 10 items are measuring the same underlying construct—perceived usability.
It also demonstrates good test-retest reliability, meaning users tend to give similar scores when tested under similar conditions. This makes it suitable for longitudinal studies and iterative design testing.
Furthermore, SUS correlates well with other usability metrics, such as task completion rates and user satisfaction scores, reinforcing its validity as a holistic usability indicator.
Speed and Simplicity in Data Collection
In fast-paced development environments, time is a critical factor. The SUS can be completed in under 5 minutes, making it ideal for integration into usability tests without burdening participants.
Its brevity increases response rates and reduces survey fatigue, especially when combined with other longer questionnaires. Users are more likely to complete a short, focused survey than a lengthy one.
For product teams, this means faster turnaround on feedback. Instead of waiting weeks for detailed usability reports, teams can get a quick usability snapshot within hours of a test session.
This agility supports agile and lean UX methodologies, where rapid iteration and continuous improvement are key.
Cross-Industry Applicability
Unlike some usability tools that are tailored to specific domains, the SUS is remarkably versatile. It has been successfully applied in:
- Software and mobile apps
- Medical devices and healthcare systems
- Automotive infotainment systems
- E-commerce websites
- Government portals
- IoT devices and smart home technology
This broad applicability stems from its focus on general usability principles rather than domain-specific features. As long as users interact with a system, SUS can assess their experience.
For example, the FDA has referenced SUS in guidance documents for evaluating the usability of medical devices, highlighting its credibility in high-stakes environments.
Limitations and Criticisms of the System Usability Scale
Despite its many strengths, the System Usability Scale is not without limitations. Understanding these weaknesses is essential for using SUS effectively and avoiding misinterpretation of results.
What SUS Doesn’t Measure
The SUS is excellent at providing a global usability score, but it doesn’t tell you *why* users gave that score. It lacks diagnostic power—meaning it won’t pinpoint specific usability issues like navigation problems, unclear labels, or broken workflows.
For example, a low SUS score could result from poor information architecture, slow performance, or confusing terminology. Without additional qualitative data, you won’t know which factor is to blame.
This is why SUS should never be used in isolation. It’s best paired with methods like user interviews, heuristic evaluations, or session recordings to uncover root causes.
Subjectivity and Response Bias
Because SUS relies on self-reported data, it’s vulnerable to subjective interpretation and response bias. Users may rate a system higher if they like the brand, or lower if they’re having a bad day.
Cultural differences can also affect responses. Some cultures tend to avoid extreme ratings, leading to more neutral scores even if the experience was poor.
Additionally, users with higher technical literacy may rate a system more leniently than novices, even if the system is objectively difficult for beginners.
To mitigate this, it’s important to segment your data by user type and combine SUS with objective performance metrics.
Need for Complementary Usability Methods
To get a complete picture of usability, SUS should be part of a broader evaluation strategy. Here are some complementary methods:
- Think-aloud protocols: Capture real-time user thoughts during task execution.
- Task success rate: Measure how many users complete key tasks successfully.
- Time on task: Assess efficiency by tracking how long users take to complete actions.
- Net Promoter Score (NPS): Gauge user loyalty and willingness to recommend the product.
- Post-Study System Usability Questionnaire (PSSUQ): A more detailed alternative to SUS with subscales for satisfaction, usability, and support.
Using SUS alongside these methods creates a triangulated approach that balances quantitative and qualitative insights.
Real-World Applications of the System Usability Scale
The true value of the System Usability Scale becomes evident when we look at how it’s used in real-world scenarios across different industries. From tech giants to healthcare providers, organizations rely on SUS to make data-driven decisions about product design and user experience.
Case Study: SUS in Software Development
A leading SaaS company used SUS to evaluate the usability of its new project management tool. After conducting usability tests with 25 users, they administered the SUS and received an average score of 62—below the industry benchmark.
Further qualitative analysis revealed that users struggled with the navigation menu and found the task assignment process confusing. The development team prioritized these issues in the next sprint.
After implementing changes, they retested with another 20 users. The SUS score improved to 78—a significant jump indicating a much better user experience. This data was instrumental in securing stakeholder buy-in for further UX investments.
Application in Healthcare and Medical Devices
In healthcare, usability isn’t just about convenience—it’s a matter of safety. The FDA encourages the use of usability testing, including SUS, to ensure that medical devices are safe and effective for users.
One manufacturer of insulin pumps used SUS during human factors testing. Nurses and patients interacted with the device and completed critical tasks like setting dosage and reviewing logs.
The initial SUS score was 58, signaling usability concerns. Through iterative testing and design improvements, they raised the score to 85, demonstrating that the final product was not only safe but also easy to use under stress.
This data was included in regulatory submissions, showing compliance with usability standards.
Use in E-Commerce and Digital Platforms
E-commerce platforms live and die by conversion rates. A confusing checkout process can cost millions in lost sales. SUS helps identify friction points before they impact revenue.
A major online retailer used SUS to compare two versions of their mobile checkout flow. Version A scored 64, while Version B (with simplified form fields and clearer buttons) scored 81.
Based on this data, they rolled out Version B globally, resulting in a 15% increase in mobile conversion rates within three months.
This case shows how a simple usability score can translate directly into business outcomes.
Alternatives and Complements to the System Usability Scale
While the System Usability Scale remains the most popular usability questionnaire, it’s not the only option. Depending on your goals, other tools may offer deeper insights or better fit specific contexts.
Post-Study System Usability Questionnaire (PSSUQ)
Developed by IBM, the PSSUQ is a 16-item questionnaire that expands on SUS by measuring three dimensions: system usefulness, information quality, and interface quality.
Unlike SUS, which gives a single score, PSSUQ provides subscale scores, allowing for more detailed analysis. However, it’s longer and less widely adopted, making cross-study comparisons harder.
PSSUQ is ideal when you need granular feedback on different aspects of the user experience, especially in enterprise or information-heavy systems.
UMUX (Usability Metric for User Experience)
The UMUX is a shorter alternative to SUS, consisting of just four items. It was designed to correlate highly with SUS while being more concise.
UMUX-Lite, a two-item version, is even more streamlined and suitable for mobile or in-app surveys where space is limited.
While UMUX is faster to complete, it may lack the robustness of the full SUS, especially with small sample sizes.
For teams needing a quick pulse check, UMUX is a viable alternative, but SUS remains the preferred choice for formal evaluations.
Net Promoter Score (NPS) and SUS Combined
Some organizations combine SUS with NPS to get both usability and loyalty insights. NPS asks users how likely they are to recommend the product to others, which reflects overall satisfaction and brand perception.
When used together, a high SUS and high NPS indicate a product that is both usable and loved by users.
For example, a fintech app with a SUS of 85 and an NPS of +60 is likely delivering a superior user experience that drives retention and word-of-mouth growth.
This dual-metric approach is increasingly popular in product-led growth strategies.
What is a good System Usability Scale score?
A score of 68 is considered average. Anything above 70 is above average, 80+ is excellent, and 90+ is outstanding. However, what’s “good” depends on your industry and competitors. Always compare against relevant benchmarks.
Can I modify the SUS questions?
No. The SUS is a validated instrument, and changing the wording—even slightly—can invalidate the scoring model and make your results incomparable to established norms. Always use the original 10 items.
How many users do I need for a reliable SUS score?
You can get useful insights from as few as 5 users, but for more stable and generalizable results, aim for 20 or more. Larger samples reduce the margin of error and increase confidence in the findings.
Is the System Usability Scale free to use?
Yes. The SUS is in the public domain and free for both academic and commercial use. No permission is required, though proper citation is appreciated.
Where can I find a reliable SUS template?
Reputable sources like MeasuringU and the Nielsen Norman Group provide downloadable SUS templates and scoring calculators.
The System Usability Scale remains one of the most powerful, practical, and accessible tools in the UX researcher’s toolkit. Its ability to transform subjective user experiences into a clear, comparable metric makes it indispensable for anyone serious about improving usability. While it has limitations—particularly its lack of diagnostic detail—its strengths in reliability, speed, and cross-industry applicability far outweigh them. When used correctly and in conjunction with other methods, SUS provides actionable insights that drive better design decisions, enhance user satisfaction, and ultimately lead to more successful products.
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