How Many Interviews Are Enough?

It's the question every researcher hears: "How many interviews do we actually need?" The honest answer is nuanced, but there is solid research to guide you. This article breaks down the concept of saturation, reviews the academic evidence, and gives you practical frameworks for determining your sample size.

The Short Answer

For most qualitative research projects with a reasonably homogeneous participant group:

• 6 interviews will surface the most prominent themes
• 12 interviews will get you to thematic saturation for most topics
• 15–20 interviews may be needed for highly diverse populations or complex topics

These numbers come from real research, which we'll walk through below.

What Is Saturation?

Saturation is the point at which additional interviews stop generating fundamentally new insights. You're still hearing stories and details, but the core patterns have stabilized — new data confirms existing themes rather than introducing new ones.

The concept was introduced by Barney Glaser and Anselm Strauss in 1967 as part of grounded theory, but it's since become the standard criterion for sample adequacy across qualitative methods.

Saturation doesn't mean you've learned everything there is to know. It means the return on investment of each additional interview has dropped below a practical threshold.

What the Research Says

Guest, Bunce, and Johnson (2006)

This landmark study is the most frequently cited empirical investigation of saturation. The researchers analyzed 60 in-depth interviews from a study in West Africa and tracked when new themes emerged.

Their findings:

• 73% of all themes were identified within the first 6 interviews
• 92% of themes were identified within the first 12 interviews
• After 12 interviews, new themes emerged at a very low rate

Their recommendation: For studies with a fairly homogeneous population, a sample of 12 is generally sufficient to reach saturation for high-level thematic analysis. For more granular, detailed coding, more interviews may be needed.

Creswell (2013)

John Creswell, one of the most widely cited qualitative methodology scholars, provides the following general guidelines in his textbook Qualitative Inquiry and Research Design:

For product research, which most commonly uses semi-structured interviews with thematic analysis, the 5–25 range is relevant, with most studies falling in the 8–15 range.

Hennink, Kaiser, and Marconi (2017)

This study distinguished between two types of saturation:

1. Code saturation — the point where no new codes emerge (typically reached by 9 interviews)
2. Meaning saturation — the point where you fully understand the dimensions and nuances of each code (typically reached by 16–24 interviews)

This distinction is practically important: if you need broad themes to guide a product direction, 9–12 interviews may suffice. If you need deep understanding of a specific behavior for detailed design, you might need 16 or more.

Namey et al. (2016)

This study focused specifically on code saturation in applied health research and found that 80% of all themes were discovered within the first 8 interviews when the sample was relatively homogeneous. With more heterogeneous samples, the number increased to 16.

Factors That Affect Your Sample Size

The right number of interviews depends on several factors:

Population Homogeneity

The more similar your participants are, the faster you'll reach saturation. If you're interviewing senior product managers at enterprise SaaS companies, 8–10 interviews will likely be sufficient. If you're interviewing "anyone who has used a project management tool," you'll need many more.

Scope of Research Questions

Narrow, focused research questions saturate faster than broad, exploratory ones.

• "How do PMs at companies with 50–200 employees prioritize their backlog?" — Narrow; likely saturates by 8–10
• "How do people manage work across multiple tools?" — Broad; may need 15–20

Data Richness Per Interview

Longer, more in-depth interviews (45–60 minutes) generate richer data per session. You may need fewer interviews if each one is substantial. Short, shallow interviews (15–20 minutes) require more participants to reach the same depth.

Analysis Method

Basic thematic analysis requires fewer interviews for saturation than detailed grounded theory or phenomenological analysis. For most product research, basic to moderate thematic analysis is appropriate. Learn more in our thematic analysis guide.

A Practical Decision Framework

Here's a practical framework for deciding your sample size:

How to Know When You've Reached Saturation

In practice, you can track saturation in real time:

1. After each interview, note the new insights (things you hadn't heard before)
2. Track the rate of new themes emerging per interview
3. When 2–3 consecutive interviews produce no fundamentally new themes, you're likely at code saturation

This doesn't need to be formal. A simple tally of "new things I learned" per interview gives you a practical saturation curve.

With Koji, this process becomes even more visible — as the platform analyzes each interview, you can see themes building and stabilizing across your dataset. When the theme map stops changing meaningfully with new interviews, you know you're approaching saturation.

The Case for Starting Small

A pragmatic approach is to plan for 8 interviews initially, with the option to extend:

1. Conduct 5 interviews
2. Do a preliminary analysis — what patterns are emerging?
3. Conduct 3 more interviews
4. Check: are new themes still emerging at a meaningful rate?
5. If yes, conduct 2–4 more. If no, you're likely at saturation.

This iterative approach avoids both under-researching (too few interviews to be confident) and over-researching (diminishing returns on time investment).

Defending Your Sample Size to Stakeholders

Stakeholders from quantitative backgrounds often challenge qualitative sample sizes. Here's how to respond:

• Different purpose, different rules. Qualitative research aims for depth and understanding, not statistical generalizability. The goal is to understand why, not to measure how many.
• Cite the research. Guest et al. (2006) demonstrated that 12 interviews capture 92% of themes for a homogeneous group. This is peer-reviewed, reproducible evidence.
• Frame it practically. "After 10 interviews, we stopped hearing fundamentally new problems. Adding more interviews would add nuance but not change our strategic recommendations."
• Compare the alternatives. A survey of 500 people will tell you 73% find onboarding confusing. Ten interviews will tell you exactly why, where, and how to fix it.

Further Reading

• User Interview Guide — the complete interview methodology
• Finding Research Participants — recruit the right people for your study