Usability 101: Introduction to Usability - NN/G

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November 6, 2026 2026-11-06
This article replaces our original Usability 101, written by Jakob Nielsen in 2012. The original remains available for historical reference.
Usability refers to how easily people can successfully complete a task using an interface.
Usability has 5 important components:
The relative importance of these components depends on the product. For a tax-filing website used only once a year, learnability matters most. For a CAD desktop application that an architect uses for hours a day, efficiency matters most, because the architect will learn the system once and then will use it thousands of times.
Our self-paced course on the 10 usability heuristics will teach you how to apply these essential UX guidelines in your UI design.
Usability is not a property of the design alone. The same interface may be easy to use for one user doing one task, but hard to use for another user, a different task, or a different context.
For example, a 10-column comparison table may work well on a large monitor but poorly on a mobile phone. Likewise, a website may be perfectly legible to a 20-year-old but hard to read for a 60-year-old.
A usability claim is therefore always relative: usable for whom, for which task, and under what conditions?
Usability is not enough on its own. A design must also provide the functionality that people need.
Utility refers to whether an interface provides the features that users need.
If a product is easy to use but does not do what you want it to, it is of no value. And so is a product that can do everything you need but is too hard to use.
To be useful, a product needs to have both utility and usability.
User experience (UX) is broader than usability. It covers every aspect of a person's interaction with a company, its services, and its products — including, for example, customer support, pricing, and what happens after a purchase. Usability is just one of the qualities of a good user experience. Others include utility, accessibility, and trustworthiness.
When a website or an app is hard to use, people usually leave. If they cannot figure out what the company offers, cannot find a product, or cannot complete a form, they will likely go to a competitor or abandon the task.
When people cannot leave — for example, because they must use a government service or a product mandated by their employer — poor usability still has consequences. Users end up spending more time on tasks, making more errors, and needing more training and support. These costs are usually paid by the organization.
Usability improvements can produce substantial gains. In our 2020 analysis of redesign projects, the UX metrics that each project targeted (such as sales or signups) improved by 75% on average after a usability redesign. The results varied widely across projects, and, while the improvement figure is not a direct ROI estimate, the study showed that improvements to UX can lead to substantial gains.
The most basic and established method for improving usability is usability (user) testing. It involves recruiting representative users, asking them to perform representative tasks with the design, and then observing what they do.
For qualitative usability testing, where the goal is to find and fix problems, testing with 5 users is often sufficient to identify many of the more important usability issues in a design. Traditionally, we have recommended that teams use iterative design, which means testing a design with a small number of users, identifying and fixing usability problems, and then testing the revised design again. Start testing early with a simple prototype, before the design is implemented, and continue testing as the design evolves. The next test often reveals new usability issues.
Usability testing is not the only usability-evaluation method. Expert reviews and analytics are other common methods. Our article on when to use which UX research methods describes a broad set of user-research methods and how to choose among them.
As AI accelerates product design and implementation, usability evaluation needs to become faster. AI may enable teams to automatically identify usability problems, evaluate designs before implementation, or collect and analyze user data from live products to inform subsequent redesigns. These approaches could change the traditional process of usability evaluation through iterative design, but the same underlying principles still apply: evidence of how people interact with the design should be used to identify usability problems and improve the design.
Qualitative usability testing helps identify usability problems in an interface and understand their causes. Quantitative usability testing allows us to measure the usability of a design by collecting metrics such as:
There is no one-to-one mapping between these metrics and the five usability components. For example, time on task can be used to assess efficiency, learnability, or memorability depending on when and how it is measured.
While the exact sample size needed for a quantitative study depends on the specifics of the study, we recommend approximately 40 participants to obtain reasonably precise estimates for usability metrics.
Usability testing does not require a usability lab. Most usability studies today are remote: either moderated, with a facilitator observing via video call, or unmoderated, with participants completing tasks on their own through a testing platform that records their screen and voice. Remote testing makes it easier to recruit participants from different locations and to run studies quickly.
In-person testing is still useful when the physical context or the gestures that people make while interacting with the product matter — for example, for kiosks, physical products, or mobile apps. For an in-person session, a quiet room with a door that closes is enough.
Anyone can run a usability test, provided that they have learned the bas