The System Usability Scale (SUS) is a widely used tool for evaluating the usability of digital systems. This blog provides a practical guide to understanding and applying SUS, covering its calculation, interpretation, and benefits.
Learn how to leverage this powerful tool to assess user satisfaction, identify areas for improvement, and create seamless user experiences. Whether you’re working with websites, mobile applications, or software, this guide simplifies the process with actionable insights and tools like the SUS calculator.
Discover how SUS can enhance your usability testing and drive impactful design decisions.
What is the System Usability Scale (SUS)?
The System Usability Scale (SUS) is a standardized tool for measuring the usability of a product, service, or system. Created by John Brooke in 1986, it provides a quick and reliable method for assessing usability across various functions and contexts. It is widely used in UX design, usability testing, and user testing for digital products, mobile applications, and websites.
The SUS is a 10-item questionnaire designed to gauge user satisfaction, efficiency, and the overall usability of a system. Participants rate their level of agreement on a 5-point Likert scale ranging from “Strongly Disagree” to “Strongly Agree.”
A SUS calculator is a tool designed to help researchers, designers, and technical personnel calculate the system usability scale score without manually entering the formula. Google Forms or similar tools can distribute the SUS survey, collect responses, and export data for analysis. The calculator interprets user ratings and provides the overall usability average score in seconds. Here’s an example:
System Usability Scale (SUS) Calculator
Your SUS Score:
How the SUS is Calculated
Understanding how to easily calculate SUS score is essential for interpreting usability metrics accurately. This process involves collecting user feedback, scoring responses, and converting them into a standardized format for easy comparison
- Collecting Responses: Participants answer the SUS questionnaire, alternating between positively and negatively worded statements. For example:
“I think that I would like to use this system frequently.”
“I found the system unnecessarily complex.”
- Scoring:
- For positively worded statements, subtract 1 from the participant’s score (e.g., if the response is 4, the score becomes 3).
- For negatively worded statements, subtract the participant’s score from 5.
- Summing Scores:
Add the adjusted scores of all 10 items to get a raw total.
- Final Calculation:
Multiply the raw total by 2.5 to scale it to a range of 0 to 100.
For Example, if a participant’s adjusted scores sum to 25, the system usability score is 62.5 (25 × 2.5).
What the Result Means
The SUS score is an invaluable metric for understanding the usability of a system. Here’s how to interpret the results:
SUS Scores Below 50:
These scores signal poor usability. Systems in this range often frustrate users, exhibit inefficiencies, or fail to effectively meet user needs. To enhance usability, immediate and significant improvements are necessary.
Scores Between 50 and 70:
This range reflects average usability. While the system may not significantly hinder users, there are clear areas for improvement. Addressing inconsistencies, simplifying complex workflows, and focusing on user feedback can elevate the experience.
Scores Above 70:
A score in this range indicates good usability, with the system performing well in meeting user expectations. Scores exceeding 85 are considered excellent, representing intuitive, efficient, and enjoyable systems. These systems are often benchmarks for user experience success.
Interpreting these scores within the context of industry averages, user demographics, and specific system goals ensures actionable insights for continuous improvement.
Practical Guide to Using the SUS
To effectively utilize the SUS, follow this step-by-step guide. It ensures the survey is designed, administered, and interpreted correctly, allowing you to gain meaningful insights into system usability.
Step 1: Design Your SUS Survey
Create a SUS questionnaire using tools like Google Forms. Ensure the questions align with the original 10-item structure developed by John Brooke. Include statements like:
- “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 technical support to use this system.”
Step 2: Administer the Survey
Distribute the SUS survey to participants, aiming for a diverse user interaction with the system.
Step 3: Collect Responses
Gather responses and export the data. Use a SUS calculator or manually calculate a good SUS score using the abovementioned steps.
Step 4: Interpret Results
Analyze the scores to assess overall usability, identify areas needing attention, and compare against industry averages.
Benefits of using a System Usability Scale
The SUS offers numerous advantages, making it a valuable tool for usability assessment. Combining simplicity with reliable results makes it an effective benchmark for user experience across different platforms.
- Reliability: The SUS score is a reliable indicator of usability, even with small sample sizes.
- Efficiency: It provides quick insights without requiring participants to spend too much time.
- Versatility: The SUS can be used for websites, software, mobile devices, and various digital products.
- Comparison: SUS results allow comparisons against industry averages to identify relative strengths and weaknesses.
- Actionable Insights: The SUS can guide targeted improvements by highlighting areas of inconsistency or inefficiency.
Conclusion
The System Usability Scale is a practical tool for assessing usability across digital products, websites, and mobile applications. Using a SUS calculator, you can easily calculate the SUS score and gain actionable insights to improve user experience.
Whether you are testing new software, refining mobile apps, or ensuring your website meets user expectations, SUS provides a reliable framework for usability assessment. With its simplicity and effectiveness, the SUS remains a go-to method for UX designers, researchers, and technical professionals worldwide.
Implementing the SUS in your usability testing process ensures consistent evaluation and helps create user-centered designs that stand out in today’s competitive market. Start assessing usability today to make informed improvements and achieve higher user satisfaction.
