The System Usability Scale (SUS) is a widely-used tool in the field of user experience (UX) design that helps measure the subjective assessment of usability in a system. Developed in 1986 by John Brooke at Digital Equipment Corporation in the UK, the SUS is a ten-item attitude Likert scale that provides a global view of usability assessments. It is a simple and effective way to gauge user satisfaction and efficiency in achieving their objectives while using a system.

The SUS is especially useful in UX design because it provides a high-level subjective view of usability that can be used to compare different systems or changes to a system over time. Its one-dimensional aspect, yielding a single score on a scale of 0-100, makes it easy to compare even outwardly dissimilar systems. Moreover, the SUS is versatile enough to be used in evaluating a wide range of systems.

Recently, practitioners have suggested a two-factor orthogonal structure that scores the SUS on independent Usability and Learnability dimensions. This approach allows designers to differentiate between the ease of use of a system and the time it takes for users to learn how to use it.

Overall, the SUS is a valuable tool for UX designers because it helps evaluate the effectiveness and efficiency of a system while considering the users and the environment in which they use it. With normative data and a curved grading scale for mean SUS scores, the SUS provides designers with a reliable benchmark to compare their systems with others in the market. By utilizing the SUS in UX design, designers can improve their systems' usability, efficiency, and overall user satisfaction, which leads to better business outcomes.