What is usability?

Definition (ISO 9241-11)

Usability is the extent to which a product can be used by specific users in a specific context of use in order to achieve defined goals effectively, efficiently and satisfactorily.

Usability is a key quality feature of interactive systems. It describes how well a user can interact with a product in order to achieve their goals - without unnecessary hurdles or frustration.

The three dimensions of usability

1. Effectiveness

The extent to which users achieve their goals completely and correctly.

Example: Is an online form filled out and sent correctly?

2. Efficiency

Effort in relation to target achievement.

Example: How many steps, clicks or thought processes does a user need to complete a task?

3. Satisfaction

Subjective experience during use (e.g. confidence, enjoyment, freedom from stress).

Example: How pleasant does a user find the operation of an app?

Three dimensions of usability: effectiveness, efficiency, satisfaction — Figure 1: Dimensions of usability according to ISO 9241-11

Usability ≠ User Experience (UX)

Usability is a sub-area of the more comprehensive User Experience (UX).

Usability	User Experience
Focus on task fulfillment	Focus on holistic experience
Focused on efficiency, freedom from errors	Including emotion, trust, brand perception
Short-term use	Also before and after use

Why is Usability Important?

Economical: Good usability reduces support costs and increases conversions.
Psychological: It promotes cognitive relief, motivation and trust.
Ethical: It prevents frustration, errors and potential risks of use.
Normative: It is part of many standards (e.g. ISO 9241, EN 301 549).

Conclusion

Usability is more than just “ease of use” - it is a measurable, designable characteristic of interactive systems that directly influences the achievement of objectives, workload and user satisfaction.

It is a prerequisite for good UX - but not the same as it.