Ever wondered how companies measure whether their apps, websites, or software are actually easy to use? Enter the System Usability Scale (SUS) — a simple yet powerful tool that’s been the gold standard in usability evaluation for decades. Let’s dive into what makes it so essential.
What Is the System Usability Scale (SUS)?
The System Usability Scale, commonly known as SUS, is a 10-item questionnaire designed to assess the perceived usability of a system, product, or interface. Developed in 1986 by John Brooke at Digital Equipment Corporation, it has since become one of the most widely used tools in user experience (UX) research. Despite its age, the SUS remains remarkably relevant, thanks to its simplicity, reliability, and versatility.
Origins and Development of SUS
The SUS was born out of a need for a quick, reliable way to evaluate usability across different systems without requiring extensive resources. At the time, usability testing was often complex, time-consuming, and required specialized equipment. Brooke aimed to create a lightweight, yet effective, method that could be applied across various technologies — from software interfaces to medical devices.
Brooke’s original research involved testing the scale on a range of systems, including word processors and early computer interfaces. The goal was to develop a tool that could produce consistent, quantifiable results regardless of the specific technology being evaluated. The result was a 10-question survey that could be administered quickly and analyzed easily.
- Developed in 1986 by John Brooke
- Originally tested on office software and digital systems
- Designed for cross-platform usability assessment
“The System Usability Scale provides a ‘quick and dirty’ usability test that can be applied to a wide variety of products and interfaces.” — John Brooke, 1986
How the SUS Works: Structure and Scoring
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. After participants complete the survey, their responses are scored using a specific algorithm that converts raw answers into a single usability score between 0 and 100.
Here’s how the scoring works: For odd-numbered items (positively worded), you subtract 1 from the user response. For even-numbered items (negatively worded), you subtract the user response from 5. Then, sum all the converted values and multiply by 2.5 to get the final SUS score. This normalization ensures the score falls within the 0–100 range.
- 10 questions, 5-point scale
- Alternating positive/negative phrasing
- Final score ranges from 0 (worst) to 100 (best)
For example, if a user gives all ‘4’ responses, the calculation would be: (3+1+3+1+3+1+3+1+3+1) = 20 × 2.5 = 50 — an average score.
Why the System Usability Scale Is Still Relevant Today
Despite being over three decades old, the System Usability Scale remains a cornerstone in UX and human-computer interaction (HCI) research. Its enduring popularity stems from its balance of simplicity and effectiveness. Unlike more complex usability frameworks, SUS doesn’t require specialized training to administer or interpret, making it accessible to designers, developers, and product managers alike.
system usability scale – System usability scale menjadi aspek penting yang dibahas di sini.
Universality Across Platforms and Industries
One of the most powerful aspects of the SUS is its platform-agnostic nature. Whether you’re evaluating a mobile banking app, a medical device interface, or a government website, the SUS can be applied with minimal adaptation. This universality has made it a favorite in industries ranging from healthcare to fintech.
For instance, in healthcare, SUS is used to evaluate electronic health record (EHR) systems. A study published in BMJ Quality & Safety found that SUS scores correlated strongly with clinician satisfaction and error rates in EHR usage. Similarly, in e-commerce, companies use SUS to compare the usability of checkout flows across different platforms.
Research from the National Institutes of Health confirms that SUS is valid across diverse user populations and technological contexts.
- Used in healthcare, finance, education, and government
- Validated across cultures and languages
- Effective for both digital and physical interactive systems
“The SUS has demonstrated robust psychometric properties across a wide range of applications and user groups.” — Bangor, Kortum, & Miller, 2008
Cost-Effective and Time-Efficient Evaluation
Unlike usability tests that require observation rooms, eye-tracking equipment, or extensive user sessions, the SUS can be deployed in minutes. It can be administered via email, embedded in apps, or included at the end of a usability test. This low overhead makes it ideal for startups, agile teams, and organizations with limited UX budgets.
Moreover, because it generates a single numerical score, SUS allows for easy benchmarking over time. Teams can track how design changes impact usability by comparing SUS scores before and after a redesign. This quantitative approach supports data-driven decision-making without requiring deep statistical expertise.
- Takes less than 5 minutes to complete
- Easy to integrate into existing workflows
- Provides actionable, comparable data
How to Administer the System Usability Scale Correctly
While the SUS is simple to use, administering it correctly is crucial for obtaining reliable results. Missteps in timing, context, or participant selection can skew scores and lead to misleading conclusions. Let’s explore best practices for deploying the SUS effectively.
When to Use the SUS in the Design Process
The optimal time to administer the SUS is immediately after a user completes a set of representative tasks with the system. This ensures that their experience is fresh and contextually grounded. For example, after a participant finishes signing up for a service, navigating a dashboard, or completing a purchase, they should be prompted to fill out the SUS.
Using the SUS too early (e.g., before any interaction) or too late (e.g., days after use) can reduce the accuracy of responses. The goal is to capture the user’s immediate perception of usability, not a reconstructed memory.
system usability scale – System usability scale menjadi aspek penting yang dibahas di sini.
- Administer post-task or post-session
- Avoid delays between use and survey
- Use during usability testing, beta releases, or A/B tests
For longitudinal studies, SUS can be administered multiple times to track usability improvements across product iterations.
Who Should Take the SUS?
The SUS should be completed by actual users of the system — not stakeholders, developers, or designers. While internal teams can take the survey for self-assessment, their scores are not representative of real-world usability. To get meaningful data, recruit participants who reflect your target audience in terms of age, tech literacy, and usage patterns.
Research suggests that a sample size of 8–12 users can provide reliable SUS scores for formative evaluations. For summative assessments (e.g., comparing two versions), larger samples (20+) are recommended to ensure statistical significance.
- Target real end-users, not internal teams
- Ensure demographic and behavioral diversity
- Minimum 8 users for reliable trends
Jakob Nielsen’s research on usability testing supports small-sample effectiveness when using tools like SUS.
Interpreting System Usability Scale Scores
Getting a SUS score is just the first step — understanding what it means is where the real value lies. A score of 68 is often cited as the industry average, but context matters. A score above 70 is generally considered good, while anything above 80 is excellent. Below 60 may indicate significant usability issues.
Understanding the SUS Score Range
The SUS score ranges from 0 to 100, but not all scores are equally common. Most systems fall between 50 and 80. Here’s a general interpretation guide:
- Below 50: Poor usability — likely frustrating for users
- 50–60: Below average — needs improvement
- 60–70: Average — acceptable but not outstanding
- 70–80: Good — solid usability
- 80–100: Excellent — best-in-class user experience
It’s important to note that SUS is a relative measure. A score of 75 might be great for a complex enterprise tool but underwhelming for a consumer app like Instagram or Spotify, which aim for near-frictionless experiences.
“A SUS score is not an absolute measure of quality, but a comparative tool for tracking progress or benchmarking against competitors.” — Sauro & Lewis, 2016
Benchmarking Against Industry Standards
One of the most powerful uses of the SUS is benchmarking. By comparing your product’s SUS score to industry averages or competitor products, you can gauge your competitive position. For example, a study by Sauro and Lewis analyzed over 5,000 SUS scores and found that:
system usability scale – System usability scale menjadi aspek penting yang dibahas di sini.
- Consumer software averages ~78
- Enterprise software averages ~68
- Medical devices average ~65
- Websites average ~72
This data allows teams to set realistic goals. If you’re building a B2B SaaS platform and achieve a 75, you’re outperforming the enterprise average — a strong indicator of good UX.
MeasuringU’s SUS calculator and benchmark database is a valuable resource for contextualizing your scores.
Strengths and Limitations of the System Usability Scale
No tool is perfect, and the SUS is no exception. While it’s widely praised, understanding its strengths and weaknesses is essential for using it effectively.
Key Strengths of SUS
The SUS shines in several areas that explain its longevity:
- Reliability: Numerous studies have confirmed its internal consistency and test-retest reliability.
- Simplicity: Easy to administer, score, and interpret — even for non-experts.
- Flexibility: Can be used for digital and physical systems, software, and services.
- Comparability: Enables benchmarking across products, versions, and industries.
Its brevity also reduces participant fatigue, increasing completion rates and data quality.
Common Criticisms and Limitations
Despite its strengths, the SUS has several limitations:
- Lack of diagnostic detail: While it tells you if a system is usable, it doesn’t explain why or where problems exist.
- Subjective nature: Based on perception, not observed behavior — users may rate a system highly even if they made errors.
- No emotional or aesthetic dimensions: SUS focuses on usability, not delight, trust, or visual appeal.
- Scoring complexity: The odd-even scoring method can confuse new users.
To overcome these, many teams pair SUS with qualitative methods like interviews or think-aloud protocols.
“The SUS is best used as part of a broader usability evaluation strategy, not as a standalone solution.” — Kortum & Su
Practical Applications of the System Usability Scale
The real power of the SUS lies in how it’s applied. From startups to Fortune 500 companies, organizations use it to drive design decisions, validate prototypes, and improve user satisfaction.
system usability scale – System usability scale menjadi aspek penting yang dibahas di sini.
Using SUS in Product Development Cycles
Integrating SUS into agile development allows teams to measure usability at key milestones. For example:
- After a sprint involving UI changes
- Before and after a major redesign
- During beta testing with real users
By tracking SUS scores over time, product managers can identify trends and correlate usability with business metrics like conversion rates or support tickets.
A fintech company might use SUS to compare two onboarding flows. If Flow A scores 62 and Flow B scores 81, the data strongly supports adopting Flow B — even if both seem subjectively similar.
SUS in Academic and Clinical Research
The SUS is widely used in academic studies to evaluate new technologies. In human-computer interaction (HCI) research, it’s often the primary usability metric. In clinical settings, it helps assess the usability of medical devices, telehealth platforms, and patient portals.
For example, a 2020 study in the Journal of Medical Internet Research used SUS to evaluate a diabetes management app. The app scored 84, indicating high usability, which correlated with better patient adherence.
Read the full study here to see how SUS supports evidence-based design in healthcare.
Alternatives and Complements to the System Usability Scale
While SUS is powerful, it’s not the only usability metric available. Understanding alternatives helps you choose the right tool for the job.
Usability Questionnaires Similar to SUS
Several questionnaires offer similar functionality:
system usability scale – System usability scale menjadi aspek penting yang dibahas di sini.
- UMUX (Usability Metric for User Experience): A 4-item scale based on ISO 9241, shorter than SUS but less proven.
- UMUX-Lite: A 2-item version ideal for quick surveys.
- QUIS (Questionnaire for User Interaction Satisfaction): More detailed but longer and less portable.
- Nielsen’s Usability Attributes: Qualitative framework, not quantitative.
UMUX-Lite, for instance, correlates highly with SUS (r = 0.85) and is useful when survey length is a concern.
Combining SUS With Behavioral Metrics
To get a complete picture, combine SUS with behavioral data:
- Task success rate
- Time on task
- Error rates
- Click-through paths
For example, a user might give a high SUS score but fail to complete a key task — indicating a disconnect between perception and performance. This hybrid approach reveals deeper insights than SUS alone.
Nielsen Norman Group recommends mixed-method approaches for robust UX evaluation.
How to Improve Your System Usability Scale Score
Getting a low SUS score isn’t the end — it’s a starting point for improvement. Here’s how to turn insights into action.
Identifying Problem Areas From SUS Feedback
Since SUS doesn’t pinpoint specific issues, follow up with qualitative research:
- Conduct user interviews asking, “What made the system difficult to use?”
- Run usability tests to observe pain points
- Analyze open-ended feedback if included
For instance, if users disagree with “I found the system unnecessarily complex,” investigate navigation structure, information architecture, or feature overload.
Design Strategies to Boost Usability
Common fixes that improve SUS scores include:
system usability scale – System usability scale menjadi aspek penting yang dibahas di sini.
- Simplifying navigation menus
- Reducing form fields
- Improving error messages
- Adding tooltips or onboarding
- Ensuring mobile responsiveness
A/B testing these changes and re-measuring SUS can validate their impact.
What is the System Usability Scale?
The System Usability Scale (SUS) is a 10-item questionnaire used to measure the perceived usability of a system, product, or interface. It produces a score from 0 to 100, with higher scores indicating better usability.
What is a good SUS score?
A score above 68 is considered above average. Scores above 70 are good, and those above 80 are excellent. Below 60 may indicate usability problems.
How many people do you need for a SUS test?
For formative testing, 8–12 users are sufficient. For summative or comparative studies, 20 or more users are recommended for statistical reliability.
Can SUS be used for websites and mobile apps?
system usability scale – System usability scale menjadi aspek penting yang dibahas di sini.
Yes, the System Usability Scale is platform-agnostic and widely used for websites, mobile apps, software, and even physical devices with interactive components.
Is the SUS free to use?
Yes, the SUS is in the public domain and free for both commercial and academic use. No permission is required to administer or publish results.
The System Usability Scale remains a vital tool in the UX practitioner’s toolkit. Its simplicity, reliability, and adaptability make it ideal for measuring usability across countless contexts. While it has limitations — particularly in diagnostic depth — its value as a quick, quantitative benchmark is unmatched. When combined with qualitative insights and behavioral data, SUS empowers teams to build more usable, user-friendly products. Whether you’re a designer, developer, or researcher, understanding and applying the SUS can significantly enhance your ability to create meaningful user experiences.
Recommended for you 👇
Further Reading:
