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 measurable data—fast.
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 1986 by John Brooke at Digital Equipment Corporation, it 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.
Origins and Development of SUS
The SUS was born out of a need for a quick, reliable way to measure usability without requiring extensive resources or time. At the time, usability testing methods were often complex, expensive, and difficult to standardize. John Brooke sought to create a lightweight, yet effective, instrument that could be applied across different types of systems.
Brooke’s original research involved testing the SUS on a variety of systems, including word processors and computer terminals. The goal was not to diagnose specific usability problems but to provide a global assessment of a system’s usability. The result was a ten-question survey with a balanced mix of positive and negative statements, scored on a five-point Likert scale.
Since its inception, the SUS has been validated across hundreds of studies and translated into dozens of languages. Its enduring popularity stems from its simplicity, reliability, and ability to produce a single, standardized score that can be compared across products and industries.
Structure and Scoring Mechanism
The SUS consists of 10 statements, each rated on a five-point scale ranging from “Strongly Disagree” to “Strongly Agree.” 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.
- I found the system unnecessarily complex.
- I thought the system was easy to use.
Scoring follows a specific pattern: for odd-numbered items (positively worded), the score is the response value minus 1. For even-numbered items (negatively worded), the score is 5 minus the response value. These are summed and multiplied by 2.5 to yield a final score between 0 and 100.
“The beauty of the SUS lies in its simplicity—it gives you a reliable usability score with just ten questions.” — Jakob Nielsen, Nielsen Norman Group
This scoring method ensures that higher scores indicate better perceived usability. A score of 68 is considered average, based on extensive benchmarking data. Anything above 80 is deemed excellent, while scores below 50 suggest significant usability issues.
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Why the System Usability Scale Matters
In today’s competitive digital landscape, user experience is a key differentiator. The System Usability Scale provides organizations with a fast, cost-effective way to quantify how easy or difficult users find their products to use. Unlike observational usability testing, which requires time and expertise, SUS can be administered remotely, at scale, and integrated into existing user research workflows.
Quantifying Subjective User Experience
Usability is inherently subjective—what feels intuitive to one user might confuse another. The SUS bridges this gap by converting qualitative feelings into a quantitative metric. This allows teams to track usability improvements over time, compare competing designs, and set benchmarks for future development.
For instance, a software company might run an SUS survey before and after a UI redesign. If the average SUS score increases from 60 to 78, that’s strong evidence the redesign improved perceived usability—even if no major functional changes were made.
Because the SUS score is a single number, it’s easy to communicate across departments. Product managers, developers, and executives can all understand what a “75” means, making it a powerful tool for aligning teams around user-centered design goals.
Supporting Data-Driven Design Decisions
Design decisions are often influenced by personal preferences or assumptions. The SUS introduces objectivity by grounding those decisions in user feedback. When stakeholders debate whether a new navigation menu is easier to use, an SUS score can settle the argument.
Moreover, SUS data can be combined with other metrics—such as task success rate, time-on-task, or Net Promoter Score (NPS)—to create a holistic view of user experience. This multi-metric approach is increasingly common in UX research, where no single measure tells the whole story.
For example, a mobile banking app might have high task completion rates but a low SUS score, indicating that while users can complete tasks, they don’t find the process enjoyable or intuitive. This insight can drive refinements that go beyond basic functionality to improve overall satisfaction.
How to Administer the System Usability Scale
One of the greatest strengths of the System Usability Scale is its flexibility. It can be used in lab studies, remote testing, post-release surveys, or even embedded within apps. However, to get reliable results, it’s important to follow best practices for administration.
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Best Practices for Deployment
To ensure valid and actionable results, the SUS should be administered under consistent conditions. Ideally, users should complete the survey immediately after interacting with the system, while their experience is still fresh.
The survey can be delivered via email, web forms (e.g., Google Forms, SurveyMonkey), or integrated directly into an application. When using digital tools, ensure the interface is mobile-friendly and accessible to all users.
It’s also crucial to provide clear instructions. Users should understand that there are no right or wrong answers and that their honest feedback is valuable. Avoid leading questions or contextual cues that might influence their responses.
Timing and Context of Administration
The timing of the SUS administration significantly impacts the quality of data. Administering it too early—before users have had enough interaction—can lead to unreliable scores. Conversely, waiting too long may result in memory decay.
A common approach is to embed the SUS at the end of a usability test session. For example, after a participant completes a series of tasks on a prototype, they’re asked to fill out the SUS questionnaire. This ensures the feedback is contextually relevant.
In post-launch scenarios, the SUS can be sent to users after they’ve had a chance to explore key features. Some companies use in-app prompts that appear after a user has logged in several times, ensuring they have sufficient experience to evaluate the system meaningfully.
Interpreting System Usability Scale Scores
Getting a number is only half the battle—the real value of the SUS comes from interpreting that number correctly. Understanding what a score means in context is essential for making informed decisions.
Understanding the SUS Score Range
The SUS produces a score between 0 and 100, with no theoretical “pass/fail” threshold. However, research has established benchmarks that help interpret results:
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- 0–50: Poor usability – significant redesign likely needed
- 51–67: Below average – usability issues present but may be fixable
- 68: Average – typical score for many commercial products
- 69–79: Good – solid usability with room for improvement
- 80–100: Excellent – top-tier usability, often seen in best-in-class products
These benchmarks are based on aggregated data from thousands of SUS responses. For example, a study by Sauro and Lewis (2006) analyzed over 2,000 SUS scores and found that the mean was approximately 68, with a standard deviation of about 13.
Comparative Benchmarking with SUS
One of the most powerful uses of the SUS is comparative analysis. By testing multiple versions of a product (e.g., old vs. new, A vs. B), teams can determine which design performs better in terms of perceived usability.
For instance, a healthcare software provider might test two different patient portal interfaces. If Version A scores 62 and Version B scores 79, the data strongly supports moving forward with Version B—even if both versions have similar functionality.
Benchmarking against industry standards is also valuable. Websites in the e-commerce sector, for example, tend to average around 70–75, while enterprise software often scores lower (60–65). Knowing these norms helps organizations set realistic goals and prioritize improvements.
Advantages of the System Usability Scale
The enduring popularity of the System Usability Scale is no accident. Its widespread adoption is due to a combination of practical benefits that make it accessible and effective for both researchers and practitioners.
Simplicity and Ease of Use
One of the biggest advantages of the SUS is its simplicity. With only ten questions, it takes most users less than five minutes to complete. This low cognitive load increases response rates and reduces survey fatigue.
Unlike more complex usability instruments, the SUS doesn’t require specialized training to administer or score. A product manager with no formal UX background can easily implement it using free online templates and scoring calculators.
This accessibility makes the SUS ideal for startups, small teams, or organizations just beginning to invest in user experience research.
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Reliability and Validity Across Domains
Despite its brevity, the SUS has demonstrated strong psychometric properties. Numerous studies have confirmed its reliability (consistency of results) and validity (accuracy in measuring what it claims to measure).
It has been successfully applied across diverse domains, including:
- Web and mobile applications
- Medical devices (e.g., insulin pumps, diagnostic tools)
- Automotive infotainment systems
- Enterprise software (CRM, ERP systems)
- Consumer electronics (smart TVs, wearables)
A 2013 meta-analysis published in the Journal of Usability Studies concluded that the SUS is “one of the most robust and versatile usability questionnaires available.” Its ability to produce consistent results across cultures, languages, and technologies underscores its scientific credibility.
Limitations and Criticisms of the System Usability Scale
While the System Usability Scale is a powerful tool, it’s not without limitations. Understanding these weaknesses is crucial for using the SUS effectively and avoiding misinterpretation of results.
What SUS Doesn’t Measure
The SUS is designed to assess overall perceived usability, not specific usability problems. It won’t tell you *why* users are struggling or *where* the pain points are located in the interface.
For example, a low SUS score might indicate that users find a mobile app confusing, but it won’t reveal whether the issue lies in navigation, labeling, or response time. To uncover root causes, SUS should be paired with qualitative methods like think-aloud protocols, interviews, or heuristic evaluations.
Additionally, the SUS does not measure emotional engagement, aesthetic appeal, or long-term user satisfaction—factors that are increasingly important in modern UX design.
Common Misuses and Misinterpretations
One common mistake is treating the SUS as a diagnostic tool. Some teams see a score of 70 and assume everything is fine, without digging deeper. But a “good” score can mask underlying issues, especially if user demographics are not representative.
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Another pitfall is administering the SUS without proper context. Asking users to rate a system they’ve barely interacted with will yield unreliable data. Similarly, using SUS in isolation—without behavioral metrics—can lead to incomplete conclusions.
Finally, some organizations modify the SUS questionnaire, thinking they can tailor it to their needs. However, altering the wording or structure invalidates the scoring model and undermines comparability with established benchmarks.
Alternatives and Complementary Tools to the System Usability Scale
While the SUS remains the gold standard for usability questionnaires, several alternative and complementary tools exist. These can be used alongside SUS to gain a more comprehensive understanding of user experience.
NPS, UMUX, and Other Usability Metrics
The Net Promoter Score (NPS) measures user loyalty by asking how likely someone is to recommend a product. While not a direct usability metric, NPS correlates moderately with SUS and provides insight into overall satisfaction.
The Usability Metric for User Experience (UMUX) is a four-item questionnaire based on ISO standards. It’s shorter than SUS and focuses on usability and usefulness. A streamlined version, UMUX-Lite, uses just two questions and correlates highly with SUS.
Another alternative is the Post-Study System Usability Questionnaire (PSSUQ), developed by IBM. It’s more detailed (16 items) and assesses satisfaction with specific aspects like system usefulness, information quality, and interface quality. However, it’s longer and less portable than SUS.
When to Use SUS vs. Other Methods
The choice of metric depends on research goals. Use the SUS when you need a quick, standardized measure of overall usability that can be compared across projects.
Use UMUX-Lite when survey length is a concern (e.g., in-app micro-surveys).
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Use PSSUQ when you need granular feedback on specific usability dimensions and have the time to administer a longer questionnaire.
Use NPS when you’re interested in brand loyalty and customer advocacy, not just usability.
In practice, many organizations use a combination. For example, a UX team might collect SUS for usability, NPS for loyalty, and qualitative feedback for context—all in a single post-task survey.
Real-World Applications of the System Usability Scale
The System Usability Scale isn’t just a theoretical tool—it’s actively used by leading companies and institutions to improve real products. From tech giants to healthcare providers, SUS helps teams make better decisions grounded in user feedback.
Case Study: SUS in Software Development
A mid-sized SaaS company developing a project management tool used SUS to evaluate a major UI overhaul. Before the redesign, the SUS score averaged 58 across 50 users. After implementing a cleaner interface with improved navigation, the score rose to 76.
This 18-point increase provided clear evidence of improved usability. The product team used this data to justify the redesign to stakeholders and secure funding for further UX enhancements.
Importantly, the SUS was administered alongside task success metrics. While task completion improved only slightly (from 82% to 86%), the large jump in SUS indicated that users found the new interface much more pleasant and intuitive to use—even for tasks they could already complete.
SUS in Healthcare and Medical Devices
In high-stakes environments like healthcare, usability can be a matter of life and death. Regulatory bodies such as the FDA encourage the use of validated usability metrics, including SUS, in the evaluation of medical devices.
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One study evaluated a new infusion pump interface using SUS. Nurses completed a series of simulated tasks, followed by the SUS questionnaire. The initial prototype scored 52, prompting a redesign focused on error prevention and clarity. The revised version scored 81, indicating a dramatic improvement in perceived usability.
This case highlights how SUS can support regulatory compliance and patient safety by identifying usability flaws before a product reaches the market. You can learn more about FDA guidance on human factors in medical devices at FDA.gov.
How to Improve Your System Usability Scale Score
Getting a low SUS score isn’t the end—it’s the beginning of a journey toward better design. The key is to use the score as a diagnostic starting point and take targeted action to address usability gaps.
Identifying Key Pain Points
While SUS doesn’t tell you *what* is wrong, it signals *that* something is wrong. To identify root causes, combine SUS with qualitative research:
- Conduct user interviews to explore why certain items scored low (e.g., “I found the system unnecessarily complex”)
- Run usability tests with think-aloud protocols to observe where users struggle
- Analyze open-ended feedback often collected alongside SUS
For example, if users consistently disagree with “I felt confident using the system,” it may indicate poor error handling, unclear feedback, or lack of onboarding.
Actionable Design Improvements
Once pain points are identified, prioritize fixes based on impact and feasibility. Common improvements that boost SUS scores include:
- Simplifying navigation and information architecture
- Reducing cognitive load with clearer labels and instructions
- Improving consistency in UI elements (buttons, icons, typography)
- Adding helpful feedback (e.g., success messages, error recovery)
- Optimizing performance (slow systems feel less usable)
After implementing changes, retest with SUS to measure improvement. Iterative testing and refinement are key to achieving high usability.
What is the System Usability Scale?
system usability scale – System usability scale menjadi aspek penting yang dibahas di sini.
The System Usability Scale (SUS) is a 10-item questionnaire that measures the perceived usability of a system. It produces a score from 0 to 100, with higher scores indicating better usability. It’s widely used due to its simplicity, reliability, and broad applicability.
How is the SUS score calculated?
Each of the 10 questions is rated on a 5-point scale. Odd-numbered items are scored as (response – 1), even-numbered items as (5 – response). The total is summed and multiplied by 2.5 to get a final score between 0 and 100.
What is a good SUS score?
A score of 68 is average. Scores above 80 are considered excellent, while those below 50 indicate poor usability. However, context and industry benchmarks matter—what’s good for one product may not be for another.
Can I modify the SUS questionnaire?
No. The SUS is a validated instrument, and changing the wording, order, or scale invalidates the scoring model and undermines reliability. Use it as-is to ensure accurate and comparable results.
Is the SUS free to use?
system usability scale – System usability scale menjadi aspek penting yang dibahas di sini.
Yes. The System Usability Scale is in the public domain and can be used freely for research, commercial, or educational purposes without permission or cost.
The System Usability Scale remains one of the most effective tools for measuring perceived usability. Its blend of simplicity, reliability, and standardization makes it indispensable for UX professionals, product teams, and researchers. While it has limitations—particularly in diagnosing specific issues—it excels as a quick, comparative metric that can drive meaningful design improvements. When used correctly, alongside qualitative insights and other metrics, the SUS empowers organizations to build products that are not just functional, but truly user-friendly.
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