This judges whether a design helps users achieve specific goals in a particular context with effectiveness, efficiency, and satisfaction. It is often associated with the function of a product as well as being a characteristic of the user interface. It is a key part of the definition of ‘usefulness’ alongside utility, and is composed of five main elements.

‘Learnability’ determines how easily users can navigate and operate a product, while ‘efficiency’ comes from how quickly they can perform those tasks once they have learned the design. The ‘memorability’ comes from the ease of returning to the design after not using it for a while, and there is the ‘satisfaction’ that comes from how pleasant the design is to use. It is also important to monitor how many ‘errors’ users make, taking into account the impact of these and how easy it is to recover.

There are two main ISO standards for usability: ISO/TR 16982:2002 on the ergonomics of human-system interaction – usability methods supporting human-centered design; and ISO 9241 on the Ergonomics of Human System Interaction.