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How many users do you actually need for a usability study?

In this episode of The Design Psychologist, Thomas Watkins talks with Laura Faulkner about one of the most repeated ideas in UX research: that five users are enough. Laura explains why that rule of thumb can be useful in some situations, but dangerous when teams treat it like a law.

They discuss sample size, research risk, stakeholder alignment, and why the real question is not “How many users?” but “What decision are we trying to support, and what happens if we miss something important?”

Laura also shares practical advice on making research more influential inside organizations: sharing early and often, treating research as community property, helping stakeholders take ownership of findings, and building a point of view from human data rather than personal opinion.

The conversation also explores synthetic users and AI, including where AI can help researchers think through test plans and where teams still need fresh data from real people.

If you want to design better studies, communicate findings with more impact, and help research actually change product decisions, this episode gives you a grounded, human-centered way to think about evidence, risk, and influence.

If today’s conversation helped you think more deeply about your work, I’d love it if you left a quick rating or review on Apple, Spotify, or your favorite podcast listening app. It helps more thoughtful designers discover the show—and keeps these meaningful insights coming your way. Just a star rating or a sentence or two makes a big difference. Thanks for listening! 

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