The System Usability Scale (SUS) is a popular measurement tool for perceived usability. It consists of a 10-item Likert scale questionnaire, where participants' responses for the 10 five-level items range from 'Strongly disagree' to 'Strongly agree'. The results are then calculated into a single 0 - 100 score, the SUS score. The sample average of several SUS scores is called the SUS study score. This SUS study score can be used for the usability evaluation of systems that requires any amount of human interaction as well as comparative usability studies, e.g. comparing the usability of interaction techniques by comparing multiple SUS study scores.

The SUS questionnaire is straightforward in its application for researchers and usability practitioners, validated through years of research and its application, available in numerous variants and languages (see our SUS PDF Generator), and easy to understand for participants.

Throughout the years, researchers proposed approaches to contextualize SUS scores, trying to answer the question of what a specific SUS study score actually means. As they follow neither a normal nor a uniform distribution, they cannot be interpreted linearly, making it challenging to interpret them directly. Consequently, researchers calculated percentile curves of SUS scores from SUS study datasets, tried to contextualize SUS scores on adjectives, grading, net promoter score, quartile and acceptability scales, calculated at which point SUS scores become conclusive, and investigated the dimensionality of the SUS questionnaire.