Have you ever wondered how top designers, researchers, and product developers consistently create user-friendly, efficient, and enjoyable products? The answer lies in the system usability scale (SUS), a key tool in the world of user experience (UX) research and evaluation.
The SUS is a questionnaire-based method to assess the usability of a system or product through a series of standardized questions. It has become an indispensable component in the realm of UX, shedding light on the user-friendliness and overall quality of digital platforms. However, the scope of the SUS extends beyond UX.
The System Usability Scale (SUS) actively plays a pivotal role in other industries, too, including technology, healthcare, e-commerce, finance, education, and automotive. SUS optimizes digital interfaces, enhances healthcare records and devices, streamlines e-commerce platforms, and improves financial systems. It refines learning experiences in education, enhances in-car interfaces in the automotive industry, and aids governments in civic engagement platforms.
Whether you’re a novice in UX research or a seasoned expert, the insights shared in this blog will empower you to harness the full potential of the system’s usability scale. You will also learn what role SUS, along with other usability scales, plays in the vast landscape of UX.
What is a System Usability Scale?
Created by John Brooke in 1986, the System Usability Scale (SUS) is a widely used tool for evaluating the usability of software, websites, and other interactive systems. Since then, it has become a standard method for assessing the overall user-friendliness of a product.
This video explores the vital connection between accessibility and usability, emphasizing the importance of designing products that are accessible to all users, thereby enhancing overall usability.
Definition of SUS
SUS is a questionnaire-based instrument designed to measure the perceived usability of a system. It consists of ten statements related to a user’s experience with a particular product, along with a five-point Likert scale. Further, respondents express their level of agreement or disagreement with these statements. The goal is to gather quantitative data that can help gauge how user-friendly a system is from the user’s perspective.
Why is SUS required?
SUS provides real-time feedback along with other critical benefits.
1. Enhances User-Centered Evaluation
SUS is pivotal in ensuring that software and interactive systems align with their users’ needs and expectations. It places a strong emphasis on the user’s perspective, making it an integral component of user-centered design and evaluation.
2. Provides Quantitative Measurement
By employing a standardized questionnaire and a numerical rating system, SUS facilitates quantitative analysis. This data allows for direct comparisons of the usability of different systems, tracks improvements over time, and sets measurable usability benchmarks.
3. Offers Speed and Simplicity
SUS is renowned for its simplicity and brevity. Consisting of just ten questions, it enables quick administration, rendering it an efficient approach for collecting usability data.
4. Facilitates Iterative Design
The speed at which SUS can be administered enables iterative design processes to run smoothly. It allows for frequent usability assessments and rapid adjustments to user interfaces, resulting in more user-friendly systems.
5. Supports Decision-Making
With SUS, decision-makers can rely on concrete, data-driven insights to make informed choices regarding software and interactive system improvements. It empowers them to prioritize enhancements that will have a major impact on user satisfaction and overall usability.
6. Enhances Collaboration
SUS can be employed as a common language for communication between designers, developers, and users. Its straightforward and numerical results make it easier for all stakeholders to discuss and address usability issues, fostering a collaborative atmosphere for ongoing system refinement.
7. Promotes Consistency
The standardized nature of SUS ensures consistency in usability evaluations across different systems and over time. This consistency is essential for tracking progress and making objective comparisons, which ultimately leads to more reliable insights and decision-making.
8. Encourages User Feedback
The concise and user-friendly format of SUS encourages users to provide feedback on their experiences, thus helping organizations collect valuable insights directly from their target audience.
9. Aids in Resource Allocation
SUS data can assist in allocating resources efficiently by pinpointing specific areas of software or system functionality that require attention. This ensures that limited resources are utilized for maximum impact.
The System Usability Scale (SUS) has evolved significantly since its inception in 1986. It was initially created by John Brooke to assess the usability of Digital Equipment Corporation’s (DEC) computer hardware and software. SUS served as a proprietary tool for a specific corporate context. However, its evolution has been marked by several key developments:
Digital Revolution and Beyond
Initially, the SUS was developed to assess DEC’s computer hardware and software, reflecting the technology landscape of its time.
With the digital revolution and the proliferation of the internet, the applications of SUS expanded rapidly. It found use in evaluating websites, software applications, and various digital interfaces, adapting to the changing technology landscape.
The SUS gained popularity for its simplicity and effectiveness. This led to greater standardization in its application.
Researchers and practitioners across industries adopted the SUS, making it a widely recognized and accepted tool for usability assessment.
Over the years, the SUS transcended its initial corporate context and became a go-to tool in the toolkit of usability professionals.
Its applicability stretches across diverse sectors, including healthcare, e-commerce, finance, education, and automotive, as mentioned earlier. Its versatile nature allowed it to adapt to the unique requirements of different industries.
The SUS went beyond its English-language roots, with translations and adaptations making it accessible to a global audience. This facilitated its use in usability studies and research worldwide, further enhancing its reach and relevance.
Integration with UX Practices
With the growing importance of user experience (UX) in product and service design, the SUS seamlessly integrated into UX practices.
It became an integral part of iterative design processes, ensuring that user feedback was consistently gathered and incorporated into product improvements.
Calculating the SUS Score
To calculate the SUS score, you need to follow these steps:
1. Data Collection
Start by gathering responses from a group of users who have interacted with your system. You can do this through a SUS survey, interviews, or online questionnaires. Ensure you have at least 50-60 responses to get a reliable result.
The SUS questionnaire consists of ten statements. Each statement is rated on a 5-point Likert scale, ranging from “Strongly Disagree” to “Strongly Agree.” Users should evaluate their level of agreement with each statement based on their experience with the system. Here are the statements:
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 cumbersome 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.
3. Score Conversion
To calculate the SUS score for each respondent, follow this formula for odd-numbered statements: subtract 1 from the user’s response, and for even-numbered statements, subtract the response from 5.
Add up the scores for all ten statements to obtain the individual SUS score for each user. The score will fall within the range of 0 to 100.
Example: If a user’s responses are (4, 2, 5, 1, 3, 2, 4, 1, 5, 2), their SUS test score would be calculated as follows:
Statement 1: 4 – 1 = 3
Statement 2: 5 – 2 = 3
Statement 3: 5 – 1 = 4
Statement 4: 5 – 1 = 4
Statement 5: 3 – 1 = 2
Statement 6: 5 – 2 = 3
Statement 7: 4 – 1 = 3
Statement 8: 5 – 1 = 4
Statement 9: 5 – 1 = 4
Statement 10: 5 – 2 = 3
Total Score = 3 + 3 + 4 + 4 + 2 + 3 + 3+ 4 + 4 + 3= 33
To normalize the scores and make them comparable across different evaluations, multiply the individual score by 2.5. In our example, the normalized score would be 33 * 2.5 = 82.5.
A SUS score can range from 0 to 100, with higher scores indicating better usability. Typically, a score above 70 is considered good, while a score above 85 is excellent.
Repeat this process for all respondents and collect their individual SUS scores. This will help you evaluate the usability of your system and identify areas for improvement based on user feedback.
Here’s an actual SUS survey template that you can use to gather user feedback and assess the usability of your system.
System Usability Scale (SUS) Template
The SUS survey template is used to gather feedback on the usability of products and design. They are versatile and user-friendly.
With these surveys, you can identify shortcomings and work toward enhancing the usability of your system.
Get your free template for “System Usability Scale (SUS) Template”
Whether you’re a designer, developer, or business owner, the SUS template is a powerful tool for making data-driven decisions for a better user experience.
Five Ways to Interpret SUS Score
1. Assessing Usability through Grading
Assigning grades to SUS scores is a straightforward way to gauge the system’s usability.
Imagine a scenario where you have an SUS score of 92; in this case, you might assign it an “A+” grade, indicating an outstanding usability experience.
Conversely, if the SUS score is 55, it could be labeled as a “D,” signifying that the system’s usability falls below par.
2. Comparative Analysis with Percentiles
Utilizing percentiles enables you to understand how a specific SUS score compares to the larger dataset.
For instance, let’s say your SUS score is 80. In this case, it falls at the 80th percentile, implying that it outperforms 80% of the scores in the database.
On the other hand, if your SUS score is 40, it would be at the 10th percentile, meaning it ranks lower than 90% of the scores in the database.
3. Descriptive Adjectives for Usability
Descriptive adjectives can provide a more nuanced perspective on usability.
Suppose you have an SUS score of 90; you might aptly describe it as “Outstanding.” If the score is 68, “Satisfactory” would be an appropriate descriptor.
In contrast, an SUS score of 35 might be characterized as “Poor,” indicating significant usability issues.
4. Categorizing Usability Acceptability
Assessing acceptability based on SUS scores involves classifying usability into different categories.
If the SUS score is 75, it’s generally considered “Acceptable,” suggesting that users find the system usable.
On the other hand, an SUS score of 30 could be seen as “Unacceptable,” indicating the need for substantial improvements.
A score of 60 may fall into the “Marginally Acceptable” category, implying that while it’s usable, there is room for enhancement.
5. Linking Usability to Recommendations
Relating SUS scores to the Net Promoter Score (NPS) helps determine user likelihood to recommend a product or service.
For example, if the average SUS score for a website is 85, it likely corresponds to the “Promoter” category in NPS, meaning users are highly likely to recommend the site.
However, if the average SUS score is 45, it would align with the “Detractor” category in NPS, indicating that users are unlikely to recommend the site to others.
Pros and Cons of Using a System Usability Scale
1. Objective User Feedback
The System Usability Scale (SUS) provides a standardized questionnaire that allows you to gather objective feedback from users about the usability of your product or system. This valuable data can help you make informed decisions for improvements and optimizations.
2. Wide Applicability
SUS is versatile and can be used in various contexts, such as websites, software applications, and hardware devices. Its flexibility makes it a practical choice for evaluating the user experience across different platforms.
3. Benchmarking and Comparisons
SUS offers a benchmark for comparing the usability of different systems or iterations of the same system. By tracking changes in SUS test scores over time, you can measure the impact of design modifications effectively.
1. Limited Contextual Information
SUS is primarily a quantitative assessment tool and may lack the depth of qualitative insights into user experiences. It provides scores but doesn’t explain the motive for the rating, which in turn requires additional research for a comprehensive understanding.
2. Interpretation Challenges
SUS scores may not always be intuitive to interpret, and a score by itself may not reveal specific areas of improvement. This can make it challenging to pinpoint the exact issues that need to be addressed in the system’s design or functionality.
3. Cultural and Language Biases
SUS was initially developed in English, which can introduce cultural and language biases when used in diverse international settings. Translations and adaptations are often required to ensure the questionnaire’s effectiveness across different languages and cultures.
When deciding to implement SUS, consider your specific research goals and the potential limitations of this usability evaluation tool.
A Practical Guide to Using a System Usability Scale
Step-by-Step Guide to Using SUS
Step 1: Understand the Basics of SUS
Before you start using SUS, it’s essential to understand its fundamentals. The SUS survey is a questionnaire consisting of ten standardized questions, which are typically rated on a five-point scale. The scores are then normalized to provide a usability score ranging from 0 to 100.
Step 2: Define Your Study Objectives
To make the most of SUS, you must clearly define your study objectives. Determine what aspect of usability you want to measure and improve. Are you assessing a website, mobile app, software, or hardware device?
Setting clear objectives will help you tailor the SUS questionnaire and evaluation process to your specific needs.
Step 3: Customize the SUS Questionnaire
While you can adjust the standard SUS questionnaire to suit your needs, be mindful that these changes might impact your ability to compare results with established standards. Tailor the language and wording of the questions to align with your product or service, enhancing participant understanding and engagement.
However, remember that these modifications may limit your capacity for direct comparisons with broader datasets and standardized results. We recommend finding a balance between customization and adherence to the standard format for obtaining meaningful insights.
Step 4: Recruit Participants
Selecting the right participants is crucial for an accurate assessment. Aim for a diverse group of users who represent your target audience. Typically, a sample size of at least 15 participants is recommended for usability testing with SUS. Ensure that participants are familiar with the product or service they are evaluating.
Step 5: Administer the SUS Questionnaire
When you administer the SUS questionnaire, ensure that participants complete it under conditions that simulate real-world usage. This might involve task-based scenarios or simply using the product as they typically would. Participants should provide their feedback honestly and without external influence.
Step 6: Calculate and Interpret SUS Scores
After collecting responses, calculate the SUS test scores for each participant. SUS scores are standardized, and a score above 68 is generally considered above average. The higher the score, the better the usability. You can use the scores to compare different versions of your product or track changes in usability over time.
Practical Tips and Tricks for Using SUS
Before your main study, conduct a pilot test with a small group of participants to identify and address any issues with your questionnaire or evaluation process.
Combine with Qualitative Data
While SUS provides a quantitative measure of usability, consider supplementing it with qualitative data, such as user comments, to gain deeper insights.
Iterate and Improve
Use the SUS score as a baseline and continuously assess and improve usability. Repeat usability evaluations periodically to track progress.
Share SUS results with key organizational stakeholders to advocate for usability improvements and support decision-making.
Challenges and Common Pitfalls
While SUS is a valuable tool, it has its challenges and potential pitfalls. Here are some common issues to be aware of:
Participants may feel pressured to provide more positive feedback than they genuinely believe, leading to inaccurate results.
Poorly worded questions can confuse participants or lead to inconsistent responses. Careful questionnaire design is essential.
A small sample size can lead to less reliable results. Ensure that you have an adequate number of participants for your study.
While a higher SUS score generally indicates better usability, it’s essential to consider the context and specific user needs.
Alternative Research Methods
SUS is a versatile tool, but there are situations where alternative research methods may be more appropriate or complimentary:
Involves expert evaluators assessing a product’s usability based on recognized usability principles.
Get your free template for “How to Conduct Your Own Heuristic Evaluation”
Users vocalize their thoughts and reactions while using a product, providing insight into their thought processes.
In-depth interviews with users to gather qualitative insights and feedback.
Task Success Rate
Measuring how successfully users complete specific tasks can be a valuable alternative to assess usability.
Comparing the performance of two or more design variations to determine which one is more user-friendly.
The Take Away
Using a System Usability Scale (SUS) can be a powerful tool for evaluating the usability of your products and services. To make the most of SUS, remember these key take aways:
Define clear study objectives to align your usability assessment with your goals.
Customize the SUS questionnaire to suit your specific needs and product/service.
Recruit a diverse group of participants and administer the questionnaire under realistic conditions.
Calculate and use SUS test scores as a baseline to track usability improvements.
The next steps involve continuous improvement and using alternative research methods when necessary. Keep in mind that usability is an ongoing process. By combining quantitative and qualitative data, you can enhance the user experience of your products and services effectively.
Where to Learn More
Learn about the best practices of qualitative user research.