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 SUS is a game-changer.
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 service. Developed in the late 1980s by John Brooke at Digital Equipment Corporation, SUS has become one of the most widely adopted usability measurement tools across industries — from software and websites to medical devices and mobile apps.
Origins and Development of SUS
The SUS was first introduced in 1986 as a quick and reliable way to evaluate usability without requiring extensive user testing or complex analytics. Brooke aimed to create a tool that was both technology-agnostic and easy to administer. Unlike other usability metrics at the time, SUS didn’t require observers or specialized equipment — just a short survey.
- Originally tested on a variety of interactive systems.
- Designed to be used post-task or post-session.
- Validated across different user groups and languages.
Its simplicity and flexibility quickly made it a favorite among usability professionals. Over the decades, SUS has been translated into more than 30 languages and used in thousands of studies worldwide. You can learn more about its original development in the original research paper by John Brooke.
How SUS Works: The 10-Item Questionnaire
The core of the System Usability Scale is a set of 10 statements that users rate 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.
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 awkward 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.Each response is scored, and a simple formula is applied to calculate the final SUS score, which ranges from 0 to 100.We’ll break down the scoring process in detail later..
Why SUS Stands Out Among Usability Metrics
There are many ways to measure usability — task success rates, time-on-task, error rates, Net Promoter Score (NPS), and more. But SUS offers something unique: a standardized, subjective measure of perceived usability that’s both quick to deploy and highly reliable.
- Standardized: The same questionnaire can be used across different products and platforms.
- Subjective yet Quantitative: Captures user feelings while producing a numerical score.
- Cost-effective: Requires no special tools or training to administer.
“SUS is not just a score — it’s a snapshot of how users feel about interacting with your system.” — Usability Expert, Jakob Nielsen
Why Use the System Usability Scale?
The System Usability Scale isn’t just popular — it’s proven. Organizations across tech, healthcare, finance, and education use SUS to make informed decisions about design, development, and user experience. But why should you care?
Measuring Perceived Usability Accurately
Usability isn’t just about whether a user can complete a task — it’s about how they *feel* while doing it. SUS captures the subjective experience, which is often overlooked in purely behavioral metrics.
- It measures perceived ease of use, confidence, and learnability.
- It helps identify hidden friction points users might not explicitly report.
- It provides a benchmark for comparing different versions of a product.
For example, two users might complete the same task successfully, but one might rate the system as frustrating while the other finds it intuitive. SUS captures that difference.
Comparing Products and Iterations
One of the most powerful uses of the System Usability Scale is comparative analysis. Whether you’re A/B testing two interfaces or evaluating a redesign, SUS gives you a consistent metric to compare performance.
- Compare SUS scores before and after a UI overhaul.
- Test competitor products using the same scale.
- Track usability improvements over time.
A study by the MeasuringU research team found that SUS scores above 68 are considered above average, making it easy to benchmark your product against industry standards.
Supporting UX Design Decisions with Data
Designers often face pushback when advocating for user-centered changes. SUS provides hard data to back up design recommendations.
- Present SUS scores to stakeholders to justify redesigns.
- Use low-scoring items to pinpoint specific usability issues.
- Combine SUS with qualitative feedback for deeper insights.
For instance, if users consistently disagree with the statement “I found the system very easy to use,” it’s a clear signal that simplification is needed.
How to Administer the System Usability Scale
One of the biggest advantages of the System Usability Scale is its ease of use. You don’t need a PhD in psychology to administer it — just follow a few best practices.
When and Where to Deploy SUS
SUS can be administered at various stages of the user journey, but timing is crucial.
- Post-task: After a user completes a specific task (e.g., making a purchase).
- Post-session: At the end of a usability test or product demo.
- Post-launch: After users have had time to interact with the product.
It’s important to administer SUS while the experience is still fresh in the user’s mind. Delaying the survey can reduce accuracy.
Best Practices for Survey Distribution
How you deliver the SUS can impact response quality.
- Use digital survey tools like Google Forms, Typeform, or SurveyMonkey.
- Ensure mobile responsiveness if users are on smartphones.
- Keep the survey anonymous to encourage honest feedback.
- Limit distractions — avoid pop-ups or ads near the survey.
For in-person usability tests, you can hand out printed copies or display the survey on a tablet. For remote testing, tools like UserTesting or Lookback can integrate SUS seamlessly.
Avoiding Common Pitfalls
Even a simple tool like SUS can be misused.
- Don’t modify the questions: Changing wording invalidates the scoring model.
- Don’t skip instructions: Make sure users understand the scale (1 = Strongly Disagree, 5 = Strongly Agree).
- Don’t assume SUS replaces qualitative feedback: Always pair it with open-ended questions.
“The power of SUS lies in its consistency. Change one word, and you risk losing comparability.” — Dr. James Lewis, Human Factors Researcher
Calculating and Interpreting SUS Scores
The magic of the System Usability Scale isn’t just in collecting data — it’s in turning that data into meaningful insights. Let’s break down how to calculate and interpret your SUS score.
The SUS Scoring Formula Explained
Each of the 10 SUS items is scored differently based on whether it’s a positive or negative statement.
- For odd-numbered items (positive): Subtract 1 from the user’s response (e.g., a “4” becomes “3”).
- For even-numbered items (negative): Subtract the user’s response from 5 (e.g., a “2” becomes “3”).
Sum all the converted scores and multiply by 2.5 to get the final SUS score (0–100).
Example: If the total of adjusted scores is 34, then 34 × 2.5 = 85. A score of 85 is excellent.
What Do the Numbers Mean?
SUS scores are interpreted on a scale where:
- 0–67: Below average
- 68–79: Average
- 80–89: Good
- 90–100: Excellent
According to research by Sauro and Lewis, the average SUS score across thousands of studies is around 68. So, anything above that is a win.
Using SUS Benchmarks for Context
Benchmarks help you understand how your product stacks up.
- A score of 70 might be great for enterprise software but low for a consumer app.
- Compare against industry averages — e.g., mobile apps average ~74, while medical devices hover around 60.
- Track trends: A rising SUS score over time indicates improvement.
The MeasuringU SUS Calculator is a free tool that automates scoring and benchmarking.
Strengths and Limitations of the System Usability Scale
No tool is perfect. While the System Usability Scale is widely respected, it’s essential to understand both its strengths and weaknesses.
Advantages of Using SUS
The benefits of the System Usability Scale are numerous and well-documented.
- Reliable and Valid: Decades of research confirm its psychometric robustness.
- Quick to Administer: Takes less than 5 minutes to complete.
- Language and Culture Neutral: Works across different regions with proper translation.
- Free to Use: No licensing fees or restrictions.
Its reliability has been confirmed in studies published in journals like *International Journal of Human-Computer Interaction*.
Common Criticisms and Challenges
Despite its popularity, SUS isn’t without criticism.
- Lack of Diagnostic Detail: It tells you *that* there’s a problem, but not *where*.
- Subjective Nature: Based on perception, not actual behavior.
- No Emotional Depth: Doesn’t capture frustration, delight, or motivation.
- Scoring Complexity: Manual calculation can be error-prone.
Some researchers argue that SUS should be supplemented with other tools like the UMUX (Usability Metric for User Experience) or the SUPR-Q for a fuller picture.
When Not to Use SUS
SUS is versatile, but not always the best choice.
- For very short interactions: If users spend less than 2 minutes, SUS may not reflect true experience.
- For children or cognitively impaired users: The Likert scale may be too abstract.
- When you need granular feedback: Use task-specific questionnaires instead.
In such cases, consider alternatives like the Post-Study System Usability Questionnaire (PSSUQ) or the Single Usability Metric (SUM).
Real-World Applications of the System Usability Scale
The true test of any tool is how well it works in the real world. The System Usability Scale has been applied across diverse industries with impressive results.
SUS in Software and Web Development
From startups to Fortune 500 companies, SUS is a staple in UX evaluation.
- Used by Microsoft to evaluate internal tools.
- Adopted by Google for prototype testing.
- Integrated into agile sprints for continuous feedback.
One case study showed a SaaS company improving its SUS score from 62 to 81 after redesigning its onboarding flow — directly correlating with a 30% increase in user retention.
Healthcare and Medical Devices
In high-stakes environments like healthcare, usability can be a matter of life and death.
- Used to evaluate electronic health record (EHR) systems.
- Applied in FDA submissions for medical device approval.
- Helps reduce user error in critical care settings.
A study published in *Applied Ergonomics* found that SUS was effective in identifying usability flaws in infusion pumps, leading to design improvements that reduced medication errors.
E-Commerce and Mobile Apps
For consumer-facing products, SUS helps optimize the user journey.
- Used to compare checkout processes across e-commerce platforms.
- Helps identify friction in mobile app navigation.
- Correlates strongly with customer satisfaction and conversion rates.
One retailer increased its SUS score by 15 points after simplifying its mobile checkout, resulting in a 22% boost in completed purchases.
Enhancing SUS with Complementary Tools
While the System Usability Scale is powerful on its own, combining it with other methods can yield even deeper insights.
Pairing SUS with Qualitative Feedback
Numbers tell part of the story — user voices tell the rest.
- Add open-ended questions like “What did you find most confusing?”
- Conduct follow-up interviews with low-SUS scorers.
- Use thematic analysis to identify recurring pain points.
For example, if multiple users give a low score on “I felt very confident using the system,” ask them to explain why in their own words.
Integrating SUS with Behavioral Metrics
Combine perception (SUS) with behavior (analytics) for a complete picture.
- Correlate SUS scores with task success rates.
- Compare SUS with time-on-task or error counts.
- Use heatmaps or session recordings to validate survey responses.
A user might report high confidence (high SUS) but make repeated errors — indicating overconfidence or misleading interface cues.
Using SUS in Longitudinal Studies
Track usability over time to measure the impact of changes.
- Administer SUS monthly to a cohort of users.
- Monitor trends in scores after feature updates.
- Use statistical analysis to identify significant improvements.
Long-term SUS tracking helped a fintech app identify that a new dashboard design initially lowered usability (SUS dropped from 76 to 68), prompting a quick rollback and redesign.
Future of the System Usability Scale
Despite being over 35 years old, the System Usability Scale remains relevant — and continues to evolve.
Adaptations and Variants of SUS
Researchers have developed several SUS derivatives to address its limitations.
- UMUX (Usability Metric for User Experience): A 4-item shorter version.
- SUS-8: An 8-item streamlined alternative.
- mSUS (Modified SUS): Adjusted for mobile contexts.
While these variants offer convenience, they sacrifice some of the original’s reliability. Always validate any modified version carefully.
SUS in the Age of AI and Voice Interfaces
As technology evolves, so must usability tools.
- Researchers are exploring SUS for voice assistants like Alexa and Google Assistant.
- AI-driven chatbots are being evaluated using adapted SUS frameworks.
- Challenges include measuring perceived usability in non-visual interfaces.
Early studies suggest SUS remains applicable, though context-specific adjustments may be needed.
Will SUS Remain Relevant?
Given its track record, the answer is likely yes — with caveats.
- Its simplicity ensures continued adoption.
- Integration with automated UX testing platforms is growing.
- As long as humans interact with systems, perceived usability will matter.
“SUS is the ‘tape measure’ of usability — simple, universal, and indispensable.” — Dr. Aaron Bangor, HCI Researcher
What is the System Usability Scale used for?
The System Usability Scale (SUS) is used to measure the perceived usability of a system, product, or service. It helps organizations evaluate how easy and satisfying a user finds an interface, compare different designs, and make data-driven decisions to improve user experience.
How is the SUS score calculated?
The SUS score is calculated by adjusting responses to 10 questions (alternating positive and negative), summing the adjusted scores, and multiplying by 2.5. The final score ranges from 0 to 100, with higher scores indicating better perceived usability.
What is a good SUS score?
A SUS score above 68 is considered above average. Scores between 70–79 are good, 80–89 are strong, and 90+ are excellent. However, what’s “good” can vary by industry and context.
Can I modify the SUS questionnaire?
It’s not recommended to modify the System Usability Scale. Changing wording or structure can invalidate the scoring model and reduce reliability. If customization is needed, consider using validated derivatives like UMUX or SUS-8.
Is the System Usability Scale free to use?
Yes, the System Usability Scale is completely free to use. There are no licensing fees or restrictions, making it accessible to researchers, designers, and organizations worldwide.
The System Usability Scale remains one of the most trusted tools in the UX professional’s toolkit. Its blend of simplicity, reliability, and versatility makes it ideal for measuring perceived usability across countless applications. While it has limitations — particularly in diagnostic depth — its value is undeniable when used correctly and in context. By understanding how to administer, score, and interpret SUS, and by combining it with other methods, you can gain powerful insights into how users truly experience your products. As technology evolves, so too will the ways we apply SUS — but its core purpose will remain: to make systems more usable, one survey at a time.
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