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One of the most common questions in qualitative research is: How many participants are enough? For methods like user interviews and usability testing, the answer depends less on hitting a specific number and more on reaching insight saturation: the point at which new interviews stop revealing new information.
One approach is to start with around 5 participants and then scale up by a further 5 based on how complicated the subject matter is. You may also find it helpful to add additional participants if you’re new to user research or you’re working in a new area.
There’s no single “correct” sample size for qualitative research. The right number depends on:
In a paper titled How Many Interviews Are Enough?, authors Greg Guest, Arwen Bunce and Laura Johnson found that saturation often occurs around 12 participants for homogeneous groups e.g. people in the same role at an organization. When working with more diverse participants, a larger sample is typically required to reach saturation.
Although it may seem counterintuitive, collecting more data doesn’t always lead to better insights. In The Logic of Small Samples in Interview-Based Research, Mira Crouch and Heather McKenzie argue that qualitative studies with fewer than 20 participants often result in higher-quality data. Smaller samples make it easier for researchers to build rapport, leading to more natural conversations and deeper insights.
Another common guideline is to conduct around 5 interviews per persona. If your organization has well-defined personas, this approach can be especially useful, particularly when your product serves distinct user groups.
The scope of your research topic also affects how many participants you’ll need. If you’re working on quite a confined topic, for example, a single screen of a mobile app, you’ll likely find interviews with 5 participants to be sufficient. Moving into more complicated domains, like the entire checkout process for an online shopping app, will push up your sample size.