If you’ve ever wondered how users truly feel about a product’s ease of use, the System Usability Scale (SUS) is your golden ticket. Simple, reliable, and universally trusted, this tool 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 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
Brooke created the SUS during a time when usability testing was gaining traction but lacked standardized, scalable measurement tools. His goal was to develop a quick, reliable method to assess user experience without requiring extensive resources or time. The result was a concise 10-question survey that could be administered easily and produce consistent, comparable results.
What made SUS revolutionary was its balance between simplicity and statistical robustness. Unlike longer, more complex usability instruments, SUS could be completed in under 10 minutes while still delivering meaningful insights. Over the decades, it has been validated across countless studies and translated into more than 30 languages, cementing its global relevance.
How SUS Differs From Other Usability Metrics
While many usability assessment tools exist—such as the NASA-TLX (Task Load Index), UMUX (Usability Metric for User Experience), and SUPR-Q (Standardized User Experience Percentile Rank Questionnaire)—SUS stands out for its brevity, neutrality, and broad applicability.
Brevity: At just 10 questions, SUS is significantly shorter than most alternatives.Neutrality: It doesn’t favor any specific type of system or interface, making it ideal for comparing diverse products.Scalability: SUS scores can be averaged across users, sessions, or versions, enabling longitudinal tracking.
.”The beauty of the System Usability Scale lies in its simplicity.It doesn’t tell you why something is usable—it tells you how much it is usable.” — Jakob Nielsen, Nielsen Norman Group
How the System Usability Scale Works
At its core, the System Usability Scale operates on a straightforward structure: users respond to 10 statements using a 5-point Likert scale ranging from “Strongly Disagree” to “Strongly Agree.” Each statement alternates between positive and negative phrasing to reduce response bias..
After responses are collected, a standardized scoring formula calculates a final SUS score between 0 and 100. This score provides a quantitative benchmark for usability, allowing teams to compare products, track improvements over time, or validate design decisions.
The 10 SUS Questions Explained
Each of the 10 items in the SUS questionnaire plays a specific role in assessing different aspects of usability. Here’s a breakdown of each question and what it measures:
1.I think that I would like to use this system frequently.– Measures user satisfaction and willingness to engage repeatedly.2.I found the system unnecessarily complex.– Assesses perceived complexity; negatively worded.3.I thought the system was easy to use.– Directly evaluates ease of use, a core component of usability.4.I think that I would need the support of a technical person to be able to use this system.– Gauges self-sufficiency and intuitiveness.5.I found the various functions in this system were well integrated.– Evaluates consistency and cohesion across features.6..
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I thought there was too much inconsistency in this system.– Another negatively worded item focusing on interface uniformity.7.I would imagine that most people would learn to use this system very quickly.– Assesses learnability and onboarding efficiency.8.I found the system very awkward to use.– Measures user comfort and interaction fluency; negatively phrased.9.I felt very confident using the system.– Reflects user confidence and perceived control.10.I needed to learn a lot of things before I could get going with this system.– Evaluates initial learning curve; negatively worded.Notice how odd-numbered questions are positively framed, while even-numbered ones are negatively worded.This counterbalancing helps minimize the impact of acquiescence bias—where users tend to agree with statements regardless of content..
Scoring the System Usability Scale
Calculating a SUS score involves a systematic process that ensures consistency across evaluations. Here’s how it works step-by-step:
- For **odd-numbered items** (positive statements), subtract 1 from the user’s response (which ranges from 1 to 5).
- For **even-numbered items** (negative statements), subtract the user’s response from 5.
- Sum the converted values across all 10 items.
- Multiply the total by 2.5 to normalize the score to a 0–100 scale.
For example, if a user gives all “3” responses (neutral), the raw sum would be 25, and after multiplying by 2.5, the final SUS score is 62.5—right around the average benchmark.
You can automate this calculation using tools like MeasuringU’s online SUS calculator, which streamlines data processing for researchers and UX teams.
Why the System Usability Scale Is So Widely Used
The enduring popularity of the System Usability Scale isn’t accidental. Its widespread adoption stems from a powerful combination of practical advantages that make it accessible, reliable, and effective for both academic research and real-world product development.
Speed and Simplicity in Data Collection
One of the biggest reasons SUS remains a go-to tool is its speed. In under 10 minutes, participants can complete the survey, making it ideal for integration into usability tests, beta programs, or post-task feedback sessions.
Unlike lengthy interviews or observational studies, SUS doesn’t require specialized facilitators or extensive training to administer. This makes it perfect for startups, agile teams, and organizations with limited UX budgets. Whether you’re testing a prototype or launching a new app feature, SUS delivers fast insights without slowing down development cycles.
Reliability and Validity Across Contexts
Despite its simplicity, SUS has demonstrated strong psychometric properties. Numerous studies have confirmed its internal consistency (Cronbach’s alpha typically > 0.9), test-retest reliability, and construct validity.
Research published in the Journal of Usability Studies shows that SUS performs consistently across different domains—including web applications, mobile apps, kiosks, and enterprise software. This cross-context reliability means a SUS score from a healthcare app can be meaningfully compared to one from an e-commerce platform.
For deeper validation, see the seminal paper: “The System Usability Scale: Evaluation of Its Reliability and Applicability”.
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Universality and Language Neutrality
SUS has been translated into dozens of languages—including Spanish, Mandarin, Arabic, and Russian—while maintaining its psychometric integrity. This universality allows global teams to deploy SUS across international user bases with confidence.
Moreover, because the questions are generic and avoid technical jargon, SUS works equally well for tech-savvy users and novices. It doesn’t assume prior knowledge of UX terminology, making it inclusive and broadly applicable.
Interpreting System Usability Scale Scores
A SUS score alone isn’t useful unless you know how to interpret it. The magic of SUS lies not just in generating a number, but in understanding what that number means in context.
The SUS Grade Scale and Benchmarks
While SUS scores range from 0 to 100, they aren’t arbitrary. Over the years, researchers have established benchmarks to help interpret results:
- Below 50: Poor usability. Users are likely frustrated and may abandon the system.
- 50–60: Marginal. The system functions but has significant usability issues.
- 60–70: Acceptable. Meets basic expectations but has room for improvement.
- 70–80: Good. Users find the system intuitive and efficient.
- 80–90: Excellent. High user satisfaction and ease of use.
- 90–100: Outstanding. Rare and exceptional usability.
According to data compiled by Sauro and Lewis (2006), the average SUS score across thousands of studies is approximately 68. So, scoring above 70 puts your product in the top half of all evaluated systems.
Comparing SUS Scores Across Products
One of SUS’s greatest strengths is its ability to enable apples-to-apples comparisons. Because the scale is standardized, you can compare the usability of a mobile banking app to a smart home dashboard—even if they’re built by different companies.
For example, a study comparing two e-learning platforms found SUS scores of 64 and 78, respectively. Despite both being functional, the 14-point gap signaled a clear usability advantage for the higher-scoring platform, guiding redesign priorities.
This comparative power makes SUS invaluable during competitive analysis, A/B testing, or vendor selection processes.
Using SUS for Longitudinal Tracking
SUS isn’t just for one-off evaluations. Teams can use it to track usability improvements over time. By administering SUS before and after a redesign, you can quantify the impact of UX changes.
Imagine a SaaS company that scores a 58 on SUS for its legacy dashboard. After a usability overhaul, the same users retake the survey and score it 76. That 18-point jump isn’t just statistically significant—it’s a compelling business story about improved user experience.
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Longitudinal tracking also helps justify UX investments to stakeholders by showing measurable ROI on design initiatives.
Practical Applications of the System Usability Scale
The System Usability Scale isn’t just a theoretical tool—it’s actively used in real-world scenarios across industries. From tech startups to government agencies, SUS helps teams make informed decisions based on user feedback.
UX Research and Product Design
In user experience research, SUS is often integrated into usability testing protocols. After participants complete tasks (e.g., booking a flight, setting up an account), they’re asked to fill out the SUS questionnaire.
The resulting score helps UX designers identify whether the overall experience is smooth or frustrating. When combined with qualitative feedback (e.g., think-aloud protocols), SUS provides both quantitative and qualitative insights.
For instance, a fintech app might score 62 on SUS. While not terrible, it’s below average. Follow-up interviews might reveal that users struggle with navigation—prompting a redesign of the menu structure.
Healthcare and Medical Device Testing
In regulated environments like healthcare, usability isn’t just about convenience—it’s a matter of safety. The FDA recommends using validated tools like SUS to assess medical device usability.
A glucose monitoring app used by diabetic patients must be intuitive, especially for elderly users. Administering SUS during clinical trials helps manufacturers ensure that the device is not only functional but also easy to use under stress.
Studies show that medical devices with SUS scores above 75 have lower error rates and higher patient compliance, directly impacting health outcomes.
Enterprise Software and Internal Tools
Even internal systems benefit from SUS evaluation. HR portals, inventory management software, and CRM platforms all affect employee productivity and satisfaction.
A large corporation might roll out a new HR system and use SUS to gauge employee sentiment. If the average score is 55, leadership knows there’s a problem—even if the system is technically “working.” This feedback can drive training improvements, UI tweaks, or even vendor renegotiations.
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Limitations and Criticisms of the System Usability Scale
No tool is perfect, and the System Usability Scale is no exception. While its strengths are undeniable, understanding its limitations is crucial for responsible use.
Lack of Diagnostic Detail
SUS tells you how usable a system is, but not why. A low score indicates problems, but it doesn’t pinpoint whether the issue lies in navigation, terminology, layout, or performance.
To get actionable insights, SUS should be paired with other methods—such as user interviews, heatmaps, or task success rates. Think of SUS as the “vital signs” of usability: it tells you if the patient is healthy, but you need further tests to diagnose the illness.
Sensitivity to Context and User Expectations
SUS scores can be influenced by factors outside the system itself. For example, users who are already familiar with similar tools may rate a new system higher due to transfer learning. Conversely, users under time pressure or stress may give lower scores, even if the interface is well-designed.
Additionally, cultural differences in response tendencies (e.g., some cultures avoid extreme ratings) can affect scores. While SUS is robust, these contextual nuances must be considered during interpretation.
Generic Nature May Miss Domain-Specific Issues
Because SUS uses generic language, it may overlook domain-specific usability challenges. For instance, a video editing tool might have excellent overall usability (high SUS score) but poor performance in advanced features like color grading—something SUS wouldn’t capture.
In such cases, supplementing SUS with domain-specific questionnaires (e.g., the Video Editing Usability Inventory) provides a more complete picture.
Best Practices for Using the System Usability Scale
To get the most out of the System Usability Scale, it’s essential to follow best practices in administration, analysis, and interpretation.
When and How to Administer SUS
SUS should be given immediately after a user completes a set of representative tasks. This ensures that their experience is fresh and contextually grounded.
Administer it at key milestones:
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- After usability testing sessions
- Post-launch of a new feature
- Before and after major redesigns
- During beta testing phases
Avoid using SUS as a standalone survey without any interaction—it loses meaning if users haven’t actually used the system.
Combining SUS With Other UX Metrics
SUS shines brightest when used alongside complementary metrics. Consider pairing it with:
- Task Success Rate: What percentage of users completed key actions?
- Time on Task: How long did it take to complete tasks?
- Net Promoter Score (NPS): Would users recommend the system?
- Qualitative Feedback: What did users say during interviews?
This multi-method approach gives a 360-degree view of usability, turning data into actionable strategy.
Reporting and Acting on SUS Results
Collecting SUS data is only half the battle. The real value comes from sharing insights and driving change.
When reporting results:
- Include the average SUS score with standard deviation.
- Compare it to benchmarks (industry average, previous version, competitors).
- Highlight trends over time with visual charts.
- Pair scores with quotes or observations for context.
Then, translate findings into design sprints, roadmap priorities, or training programs. SUS isn’t just a metric—it’s a catalyst for improvement.
Alternatives and Complements to the System Usability Scale
While SUS is powerful, it’s not the only usability measurement tool available. Depending on your goals, you might consider alternatives or complementary frameworks.
UMUX and UMUX-Lite
The Usability Metric for User Experience (UMUX) is a 4-item scale based on ISO standards for usability (ISO 9241-11). It focuses on effectiveness, efficiency, and satisfaction.
UMUX-Lite, a 2-item version, is even shorter than SUS and correlates highly with it (r > 0.9). It’s ideal when survey length is a critical constraint.
Learn more at: MeasuringU’s UMUX Guide.
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SUPR-Q: Website-Specific Usability
The Standardized User Experience Percentile Rank Questionnaire (SUPR-Q) measures four key aspects of website UX: usability, trust, loyalty, and appearance.
Unlike SUS, SUPR-Q provides percentile rankings based on a large benchmark database, making it especially useful for e-commerce and content sites.
NPS and CSAT for Broader Satisfaction
While not direct usability metrics, Net Promoter Score (NPS) and Customer Satisfaction (CSAT) offer insights into overall user sentiment. Used together with SUS, they help distinguish between usability issues and broader satisfaction factors like pricing or customer service.
What is a good System Usability Scale score?
A score above 68 is considered above average, as this is the mean across thousands of studies. Scores above 70 are generally “good,” 80+ are “excellent,” and 90+ are “outstanding.” However, what’s “good” depends on your industry and competitors.
Can I modify the SUS questionnaire?
No. The SUS is a validated instrument, and altering any part of it (wording, order, scale) invalidates its psychometric properties. If you need a custom tool, consider building a new questionnaire or using a flexible framework like UMUX.
How many users do I need for a reliable SUS score?
Research suggests that as few as 5–8 users can provide a reasonably stable SUS score in usability testing. For higher precision or benchmarking, aim for 15–20 users. Larger samples (30+) are ideal for product launches or regulatory submissions.
Is the System Usability Scale free to use?
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Yes! The SUS is in the public domain and free for both commercial and academic use. There are no licensing fees or restrictions. Just ensure you cite the original source: Brooke, J. (1986). SUS: A quick and dirty usability scale.
Where can I find the official SUS questionnaire?
The original SUS questionnaire is available through academic publications and reputable UX resources. A trusted source is the Usability.gov page on SUS, maintained by the U.S. Department of Health and Human Services.
The System Usability Scale remains one of the most powerful, practical tools in the UX professional’s arsenal. Its blend of simplicity, reliability, and universality makes it indispensable for measuring how users truly experience a system. While it has limitations—particularly in diagnostic depth—its value is amplified when used alongside qualitative methods and other metrics. Whether you’re refining a mobile app, validating a medical device, or improving an internal tool, SUS provides a clear, quantifiable snapshot of usability. By understanding how to administer, interpret, and act on SUS data, organizations can make user-centered decisions that drive satisfaction, efficiency, and success.
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