Usability

Usability refers to the degree to which a product or system can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use. It is a central concern of human-computer interaction and user-centered design, and it is closely related to the broader concept of user experience (UX).

Core attributes commonly used to describe usability include: learnability, efficiency of use, memorability, low error frequency and severity, and user satisfaction. Learnability measures how easy it is for new users to accomplish basic tasks. Efficiency concerns the speed and effort required for proficient users. Memorability refers to how well returning users can reestablish proficiency after a period away. Error tolerance includes preventing errors where possible and providing clear recovery. Satisfaction reflects users' comfort and perceived quality.

Usability evaluation employs various methods: usability testing, where representative users attempt tasks in realistic settings; heuristic evaluations, where experts assess the interface against established heuristics; cognitive walkthroughs; and surveys or interviews to assess satisfaction. Common metrics include task success rate, time on task, error rate, and subjective satisfaction, often summarized with standardized scales such as the System Usability Scale (SUS).

Practices emphasize iterative, user-centered design. Early field studies and task analyses inform requirements; prototypes are tested and refined; accessibility and inclusive design are integrated to support diverse users. Design principles include consistency, appropriate feedback, visibility of system status, error prevention and helpful error messages, and alignment with user mental models.

Usability applies to software, websites, consumer electronics, industrial equipment, and services. Good usability can reduce training costs, increase productivity and adoption, and improve safety by reducing user errors. It is often addressed during the product lifecycle through usability engineering, guidelines, and standards.

Standards such as ISO 9241-11 define usability in terms of effectiveness, efficiency, and satisfaction within a context of use and guide measurement and evaluation practices.