SUS: Product Usability

What is SUS?

The System Usability Scale (SUS) is a tool used to assess the usability of products and services. It consists of a questionnaire with 10 items rated on a five-point scale, where respondents evaluate their experience using a system, product, or service. The questions cover various aspects of usability, including effectiveness, complexity, learnability, and user satisfaction.

After completing the questionnaire, the results are converted into an overall score ranging from 0 to 100. This score is not a percentage but allows assessment of the system’s overall usability. The higher the score, the better the usability. SUS is widely used due to its versatility, ease of use, and reliability. It is suitable for evaluating a broad range of products and services, including websites, applications, mobile devices, as well as more complex software and hardware.

Procedure for Conducting SUS

The SUS evaluation process involves several steps aimed at collecting and analyzing user feedback on the product or service usability. The main steps are:

• Clearly define what you want to study with SUS.
• Recruit respondents representing your target audience.
• Provide participants with clear instructions on the task.
• Allow participants to use the product or service.
• Have participants complete the SUS questionnaire after using the product.
• Convert answers into scores and calculate the overall SUS score.
• Analyze the results by calculating averages, medians, and standard deviations.
• Assess the product’s usability level based on SUS scores.
• Formulate recommendations based on the analysis.
• Prepare and present a report to stakeholders.

Instructions

Provide participants with a list of ten statements. For each, they should express their agreement using a scale from 1 (strongly disagree) to 5 (strongly agree). Odd-numbered statements are positively worded, while even-numbered ones are negatively worded:

1. I think that I would like to use this product/function/service regularly.
2. I found the product/function/service unnecessarily complex.
3. I thought the product/function/service was easy to use.
4. I think that I would need the support of a technical person to be able to use this product/function/service.
5. I found the various functions in this product/service were well integrated.
6. I thought there was too much inconsistency in this product/function/service.
7. I would imagine that most people would learn to use this product/function/service very quickly.
8. I found the product/function/service very cumbersome to use.
9. I felt very confident using the product/function/service.
10. I needed to learn a lot of things before I could get going with this product/function/service.

Answer Analysis

• Subtract 1 from the scores for the odd-numbered questions.
• Subtract the scores for the even-numbered questions from 5 (results range from 0 to 4 for each question).
• Add up all the adjusted scores for all ten questions.
• Multiply the total by 2.5 to obtain a final score ranging from 0 to 100.
• Calculate the average score across all respondents to get the overall SUS score.

What is a Normal SUS Score?

The average score considered "normal" or acceptable is around 68 out of 100. This serves as a baseline indicating that the product, function, or service has an acceptable level of usability. It is important to understand that:

• Scores below 68 may indicate a need for usability improvements.
• Scores above 68 suggest the product’s user interface is perceived as good and easy to use.
• Very high scores above 80 indicate excellent usability and high user satisfaction.