System Usability Scale: 10 Powerful Insights You Must Know

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Ever wondered how companies measure how user-friendly their products really are? Enter the System Usability Scale (SUS)—a simple yet powerful tool that reveals the truth behind user experience. Let’s dive into why it matters and how it works.

What Is the System Usability Scale (SUS)?

The System Usability Scale, commonly known as SUS, is a widely used, reliable method for measuring the perceived usability of a system, product, or service. Developed in the late 1980s by John Brooke at Digital Equipment Corporation, SUS has since become a gold standard in usability evaluation 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, cost-effective way to assess usability without requiring extensive user testing or complex analytics. Unlike other subjective scales, SUS was designed to be technology-agnostic, meaning it can be applied to virtually any interactive system, regardless of platform or function.

Created by John Brooke during usability research at Digital Equipment Corporation.
Originally intended for internal use but quickly gained traction in academic and industry circles.
Published in a 1996 conference paper, which helped cement its place in usability literature.

Its simplicity and flexibility made it a favorite among UX researchers, leading to widespread adoption across global organizations. You can read the original research paper here.

How the SUS Questionnaire Works

The SUS consists of 10 statements, each rated on a five-point Likert scale ranging from “Strongly Disagree” (1) to “Strongly Agree” (5). The statements alternate between positive and negative phrasing to reduce response bias.

Odd-numbered items are positively worded (e.g., “I thought the system was easy to use”).
Even-numbered items are negatively worded (e.g., “I found the system unnecessarily complex”).
Users score each item, and a specific formula is used to calculate the final SUS score.

This balanced design helps ensure that users pay attention and don’t just agree with everything automatically—a common issue in survey design.

The SUS Scoring Mechanism Explained

After users complete the 10-item questionnaire, their responses are processed using a standardized formula to produce a single number between 0 and 100. This score represents the overall usability of the system.

For odd-numbered items: Subtract 1 from the user response (so a “5” becomes “4”).
For even-numbered items: Subtract the user response from 5 (so a “1” becomes “4”, a “2” becomes “3”, etc.).
Sum all adjusted values and multiply by 2.5 to get the final SUS score.

“The beauty of the System Usability Scale lies in its simplicity. With just 10 questions, you can get a reliable snapshot of how usable your product feels to real users.” — Jakob Nielsen, UX Pioneer

For example, if a user gives all “3” responses (neutral), the total adjusted sum would be 25, multiplied by 2.5 equals 62.5—a baseline score indicating average usability.

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 combination of practical advantages that make it ideal for both academic research and real-world product development.

Speed and Simplicity in Data Collection

One of the biggest strengths of the SUS is how quickly it can be administered. Most users complete the questionnaire in under 5 minutes, making it easy to integrate into usability tests, beta programs, or post-task feedback sessions.

Minimal time burden on participants increases response rates.
Can be embedded directly into apps, websites, or post-session surveys.
Requires no specialized training to administer—ideal for startups and small teams.

This efficiency allows teams to gather usability data at scale, even with limited resources.

Reliability and Validity Across Contexts

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).

High internal consistency, with Cronbach’s alpha typically above 0.9.
Validated across diverse domains: healthcare, finance, e-commerce, education, and more.
Consistent performance across languages and cultures when properly translated.

A landmark study by Bangor, Kortum, and Miller (2008) confirmed that SUS produces stable, meaningful results across different user groups and technologies. You can explore their findings here.

Cost-Effectiveness for UX Teams

Unlike complex usability labs or eye-tracking studies, the SUS requires no special equipment or software. It’s completely free to use, with no licensing fees or restrictions.

Open access: Anyone can download and implement the SUS questionnaire.
Reduces dependency on expensive third-party tools.
Perfect for agile environments where rapid iteration is key.

This democratizes usability testing, allowing even small organizations to benchmark their products against industry standards.

How to Administer the System Usability Scale Correctly

While the SUS is simple to use, getting accurate and meaningful results depends on proper administration. Missteps in timing, context, or interpretation can lead to misleading conclusions.

Best Practices for Timing and Context

When you administer the SUS can significantly affect the results. Ideally, it should be given immediately after a user completes a set of representative tasks with the system.

Post-task administration captures fresh, context-specific impressions.
Avoid administering SUS too early (before meaningful interaction) or too late (after memory fades).
For longitudinal studies, SUS can be administered multiple times to track usability improvements.

For example, after a user finishes signing up for a service or completing a purchase, that’s the perfect moment to ask them to rate the system’s usability.

Avoiding Common Pitfalls in SUS Implementation

Despite its simplicity, there are several common mistakes that can compromise SUS data quality.

Using SUS in isolation: While SUS gives a great overall score, it doesn’t explain why users feel a certain way. Always pair it with qualitative feedback.
Misinterpreting the score: A score of 68 doesn’t mean “68% usable”—it’s a normalized index, not a percentage.
Changing the wording: Altering the SUS statements invalidates the scoring model and makes comparisons unreliable.

Sticking to the original 10 items and standardized scoring is crucial for maintaining consistency and comparability.

Integrating SUS Into User Testing Workflows

The System Usability Scale works best when embedded into a broader user research strategy. It should complement, not replace, other usability methods.

Use SUS at the end of moderated or unmoderated usability tests.
Pair it with task success rates, time-on-task, and error rates for a holistic view.
Automate SUS collection using survey tools like Qualtrics, SurveyMonkey, or UserTesting.

For instance, after observing a user navigate a new app interface, the facilitator can say: “Now that you’ve completed the tasks, we’d like your feedback on how easy or difficult the system was to use.” Then present the SUS form.

Interpreting System Usability Scale Scores Accurately

Getting a number is only half the battle—understanding what that number means is where the real value lies. The SUS score is more than just a metric; it’s a benchmark for decision-making.

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Understanding the SUS Score Range (0–100)

The SUS produces a score between 0 and 100, but not all scores are created equal. While there’s no universal “pass/fail” threshold, researchers have established general guidelines for interpretation.

Below 50: Poor usability—significant redesign likely needed.
50–60: Marginal—some usability issues present.
60–70: Acceptable—meets basic usability expectations.
70–80: Good—users find it reasonably easy to use.
80–90: Excellent—highly usable, competitive advantage.
90–100: Outstanding—rare, often seen in best-in-class products.

According to research by Sauro and Lewis (2016), the average SUS score across thousands of studies is around 68, making it a useful benchmark for comparison.

Benchmarking Against Industry Standards

One of the most powerful uses of the SUS is benchmarking—comparing your product’s score against competitors or industry averages.

Software applications average around 68–72.
Mobile apps tend to score slightly higher, often in the 70–75 range.
Medical devices, due to regulatory complexity, often score lower (55–65).
Top consumer apps like Google Search or Amazon routinely score above 80.

By comparing your SUS score to these benchmarks, you can gauge your product’s competitive position and prioritize improvements.

What a High or Low SUS Score Really Means

A high SUS score doesn’t just mean users “liked” the system—it reflects efficiency, learnability, and overall satisfaction. Conversely, a low score signals friction, confusion, or frustration.

High scores often correlate with lower support costs, higher conversion rates, and increased user retention.
Low scores may indicate poor information architecture, unclear navigation, or inconsistent design patterns.
Even a small improvement (e.g., from 65 to 75) can have a significant impact on user behavior.

However, remember: SUS tells you how usable your system is, but not why. That’s where follow-up questions or interviews come in.

Strengths and Limitations of the System Usability Scale

No tool is perfect, and the System Usability Scale is no exception. While it’s one of the most trusted usability metrics, understanding its limitations is key to using it effectively.

Advantages That Make SUS a Go-To Tool

The System Usability Scale has earned its reputation through consistent performance and practical benefits.

Brevity: Only 10 questions minimize respondent fatigue.
Standardization: Enables direct comparison across products, versions, and studies.
Proven track record: Used in thousands of studies worldwide with consistent results.
Free to use: No cost or legal barriers to implementation.

These advantages make SUS a cornerstone of modern UX evaluation frameworks.

Criticisms and Common Concerns

Despite its strengths, the SUS has faced criticism from some researchers and practitioners.

Lack of diagnostic detail: Doesn’t pinpoint specific usability problems.
Subjective nature: Based on perception, not objective performance.
Neutral midpoint bias: Some users tend to choose middle options, skewing results.
Not ideal for all audiences: May be challenging for children or cognitively impaired users.

Additionally, because SUS is a global measure, it doesn’t differentiate between dimensions like learnability, efficiency, or satisfaction—though it reflects them collectively.

When Not to Use the System Usability Scale

While versatile, the SUS isn’t always the best choice. There are scenarios where alternative or complementary tools are more appropriate.

During early prototyping: When the interface is too rough for meaningful feedback.
For accessibility evaluation: SUS doesn’t assess compliance with WCAG or assistive technology support.
When deep diagnostics are needed: Use tools like the Post-Study System Usability Questionnaire (PSSUQ) or heuristic evaluation instead.
For non-interactive systems: SUS requires user interaction; it’s not suitable for static content.

In these cases, combining SUS with other methods provides a more complete picture.

Advanced Applications of the System Usability Scale

Beyond basic usability scoring, the System Usability Scale can be used in innovative ways to drive product strategy and organizational change.

Using SUS for Product Iteration and Design Improvement

One of the most powerful applications of SUS is tracking usability over time. By measuring SUS before and after design changes, teams can quantify the impact of their work.

Run SUS before and after a redesign to measure improvement.
Compare SUS scores across different user segments (e.g., new vs. returning users).
Use SUS as a KPI in sprint retrospectives or product reviews.

For example, a fintech app that improved its onboarding flow saw its SUS score jump from 62 to 78—a clear indicator of enhanced user experience.

SUS in Academic Research and Industry Studies

The System Usability Scale is one of the most cited tools in human-computer interaction (HCI) literature. Its standardized nature makes it ideal for comparative studies.

Used in peer-reviewed journals to evaluate new interfaces, AI systems, and AR/VR environments.
Helps validate the effectiveness of usability interventions.
Enables meta-analyses across multiple studies due to consistent scoring.

Researchers often combine SUS with other metrics like the Net Promoter Score (NPS) or the Technology Acceptance Model (TAM) to explore broader user behavior patterns.

Integrating SUS Into Enterprise UX Strategies

Forward-thinking companies are embedding SUS into their UX maturity models. It’s no longer just a research tool—it’s a strategic metric.

Set internal usability benchmarks using SUS (e.g., “All new features must score ≥75”).
Train product managers and designers to interpret SUS data.
Report SUS scores in executive dashboards alongside business KPIs.

Organizations like IBM, Microsoft, and Google have used SUS at scale to maintain high usability standards across their vast product portfolios.

Alternatives and Complements to the System Usability Scale

While the System Usability Scale is powerful, it’s not the only usability metric available. Understanding its alternatives helps you choose the right tool for the job.

When to Combine SUS With Qualitative Methods

The real power of SUS emerges when combined with qualitative insights. Numbers tell you what happened; user quotes tell you why.

Follow up SUS with open-ended questions: “What did you find most confusing?”
Conduct interviews or focus groups to explore low-scoring areas.
Use think-aloud protocols during testing to capture real-time feedback.

For instance, if SUS scores drop after a redesign, qualitative feedback might reveal that users missed a familiar button—even if the new design was technically better.

Emerging Trends in Usability Measurement

As technology evolves, so do usability assessment methods. While SUS remains relevant, new approaches are gaining traction.

Behavioral analytics: Using clickstream data, heatmaps, and session recordings to infer usability.
Sentiment analysis: Applying NLP to user reviews or support tickets to detect frustration.
Biometric measures: Eye-tracking, facial expression analysis, and galvanic skin response for emotional feedback.
Automated SUS scoring tools: Platforms like UserZoom and Maze now auto-calculate SUS and provide benchmarks.

However, none have replaced SUS—many actually integrate it as a core component.

Real-World Examples of System Usability Scale in Action

The true test of any metric is how well it performs in real-world scenarios. Let’s look at how organizations across industries have successfully used the System Usability Scale.

Case Study: Healthcare Application Redesign

A telemedicine platform was struggling with low user adoption. After conducting usability tests with SUS, they found the initial score was only 54—well below the acceptable threshold.

Identified key pain points: confusing navigation, unclear appointment scheduling.
Redesigned the interface with clearer labels and a streamlined flow.
Post-redesign SUS score jumped to 79—a 25-point improvement.

This increase correlated with a 40% rise in completed appointments and a 30% drop in customer support calls.

Case Study: E-Commerce Checkout Optimization

An online retailer wanted to reduce cart abandonment. They tested two versions of their checkout process using SUS alongside conversion metrics.

Version A (original): SUS score of 63, 68% completion rate.
Version B (simplified): SUS score of 77, 82% completion rate.
Qualitative feedback confirmed users felt “less stressed” and “more in control.”

The higher SUS score predicted better business outcomes, validating the redesign.

Case Study: Enterprise Software Training Program

A global company rolled out new ERP software. To assess learnability, they administered SUS after a training session.

Initial SUS score: 58—indicating significant usability challenges.
Added tooltips, contextual help, and a guided tour.
Follow-up SUS after one month: 73.

The improved score reflected better user confidence and reduced training costs.

What is the System Usability Scale?

The System Usability Scale (SUS) is a 10-item questionnaire used to assess the perceived usability of a system. It produces a score from 0 to 100, with higher scores indicating better usability. Developed by John Brooke in 1986, it’s widely used due to its simplicity, reliability, and versatility across platforms.

How do you calculate a SUS score?

To calculate a SUS score: for odd-numbered items, subtract 1 from the response; for even-numbered items, subtract the response from 5. Sum all adjusted values and multiply by 2.5. The result is a score between 0 and 100.

What is a good SUS score?

A SUS score above 68 is considered above average. Scores from 70–80 are good, 80–90 are excellent, and 90+ are outstanding. A score below 50 indicates poor usability and the need for significant improvements.

Can I modify the SUS questionnaire?

No, the SUS should not be modified. Changing the wording, order, or number of items invalidates the scoring model and prevents comparison with established benchmarks. Always use the original 10 items to maintain reliability.

Is the System Usability Scale free to use?

Yes, the System Usability Scale is completely free to use with no licensing fees or restrictions. It’s in the public domain and can be used for academic, commercial, or internal purposes without permission.

The System Usability Scale remains one of the most effective, accessible tools for measuring user experience. Its blend of simplicity, reliability, and actionable insights makes it indispensable for UX professionals, product teams, and researchers. While it has limitations—such as not diagnosing specific issues—it excels as a benchmarking tool and a quick gauge of overall usability. When used correctly and in combination with qualitative methods, SUS provides a powerful lens into how users truly perceive a system. Whether you’re refining a mobile app, launching a new website, or evaluating enterprise software, incorporating the System Usability Scale into your workflow can lead to smarter design decisions and better user outcomes.