Per ISO 9241-11: the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use.
Definition: Per ISO 9241-11: the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use.
Usability is a precisely defined concept from the ISO 9241-11 standard. It measures the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use.
Effectiveness: Can users complete the task? This is a binary or graded measure of task success—did they achieve their goal?
Efficiency: What resources were expended? Typically measured as time on task, but can include error rates, number of clicks, or cognitive effort.
Satisfaction: How did users feel about the experience? Often captured through standardized scales like the System Usability Scale (SUS) or simple Likert-scale ratings.
Usability is a subset of User Experience, not a synonym. The ISO 9241-210 standard defines UX more broadly as "a person's perceptions and responses resulting from the use and/or anticipated use of a product"—including emotions, beliefs, preferences, and behaviors before, during, and after use.
A product can be highly usable (effective, efficient, satisfying for a task) while still having poor overall UX if it fails on other dimensions like aesthetics, trust, or emotional resonance. The terms are often conflated in casual conversation, but the distinction matters when you need to be precise about what you are measuring.
Note the phrase "in a specified context of use." Usability is not absolute—it depends on who is using the product, for what purpose, and under what conditions. A medical device might be highly usable for trained surgeons but completely unusable for patients. The context defines the criteria.
A Core Method combining all three Building Blocks: testing task completion (effectiveness and efficiency), observing behavior and non-verbal cues, and asking questions about the experience. The most comprehensive single research method.
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Per ISO 9241-210: a person's perceptions and responses resulting from the use and/or anticipated use of a product, system, or service—including emotions, beliefs, preferences, and behaviors before, during, and after use.
This term is referenced in the following articles:
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