How Many Interviews Are Enough? Qualitative Sample Size

Unlike quantitative research, qualitative sample size isn't calculated from a formula — it's justified conceptually, and "it depends" is a genuinely accurate answer if you can explain what it depends on. Here's how to actually justify a number instead of picking one out of habit.

Data saturation

The most commonly cited justification: you keep collecting data until new interviews stop producing new codes or themes. In practice, this means you can't fully predict your sample size before you start — you propose a target range and confirm (or adjust) it once you're coding data as you go, then report where saturation was actually reached.

Information power

A more recent framework (Malterud et al., 2016) that argues sample size should depend on how much relevant information each interview yields — a narrow research question, highly specific sample, and strong analytic strategy all mean you need fewer participants than a broad question with a heterogeneous sample.

Design-specific conventions

• Phenomenology — typically 5–15 participants, given the depth of individual accounts required.
• Grounded theory — typically 20–30, since theoretical saturation across categories usually requires more participants.
• Case study — often single-digit or a small number of cases, with depth of data per case mattering more than count.
• Focus groups — usually 3–6 groups of 6–10 participants each, rather than an individual-interview count.

What to actually write in your methods section

State your target range, the justification (saturation, information power, or design convention), and how you'll know you've reached it. If you're proposing before data collection, be explicit that the final number may adjust based on saturation — committees expect this in qualitative work and it's not a weakness to state it.

If your project also has a quantitative component, our free sample size calculator handles that side of a mixed-methods design.