How to Choose the Right Sample Size in UX Research

By Philip Burgess | UX Research Leader

Choosing the right sample size in UX research can make or break your study’s success. Too few participants might lead to unreliable results, while too many can waste time and resources. Finding the balance is essential to gather meaningful insights that truly reflect user behavior and preferences.

UX researcher reviewing user data on laptop

Why Sample Size Matters in UX Research

Sample size affects the accuracy and reliability of your findings. If the group is too small, you risk missing important patterns or drawing conclusions that don’t apply broadly. On the other hand, a very large sample might provide more data than necessary, increasing costs and slowing down the research process.

The goal is to select a sample size that balances statistical confidence with practical constraints like budget and timeline. This ensures your research delivers clear, actionable insights without overextending resources.

Factors to Consider When Deciding Sample Size

Several key factors influence how many participants you need:

• Research method: Qualitative studies like interviews or usability tests often require fewer participants (5-15) because they focus on deep insights. Quantitative surveys or A/B tests usually need larger samples (30-100+) to detect trends and measure significance.

• User diversity: If your product serves diverse user groups, you may need more participants to cover different demographics, skill levels, or behaviors.

• Study goals: Exploratory research can work with smaller samples to identify issues or generate hypotheses. Validation studies require larger samples to confirm findings and measure impact.

• Expected effect size: If you expect big differences in user behavior, fewer participants may suffice. Subtle differences require larger samples to detect.

• Resources and timeline: Budget, time, and access to users can limit sample size. Prioritize quality and relevance over quantity when constraints exist.

  
  

Common Sample Size Guidelines for UX Research

Here are some practical guidelines based on research type:

• Usability testing: 5-8 participants per user group often uncover 80% of usability problems. Testing more users yields diminishing returns.

• User interviews: 10-15 interviews usually reveal common themes and user needs.

• Surveys: 30-100+ responses provide enough data for basic statistical analysis, depending on population size.

• A/B testing: Hundreds or thousands of users may be needed to detect small differences in conversion rates or behavior.

  
  

These numbers are starting points. Adjust based on your specific context and goals.

How to Calculate Sample Size for Quantitative Studies

For quantitative research, you can use formulas or online calculators to estimate sample size based on:

• Confidence level: How sure you want to be about your results (usually 95%).

• Margin of error: The acceptable range of error in your results (often 5%).

• Population size: Total number of users or customers.

• Expected response distribution: The variability in responses (commonly 50% for maximum sample size).

  
  

For example, if you survey a population of 10,000 users with 95% confidence and 5% margin of error, you might need around 370 responses. Smaller populations require fewer participants.

Tips to Optimize Sample Size and Research Quality

• Segment users carefully: Focus on key user groups to avoid unnecessary expansion.

• Pilot test: Run a small pilot to check if your sample size captures enough insights.

• Combine methods: Use qualitative research to explore issues, then quantitative to validate findings.

• Recruit strategically: Target users who match your personas and research goals.

• Monitor results: Analyze data as you collect it to decide if more participants are needed.

  
  

UX researcher taking notes in a user interview

Balancing Sample Size with Practical Constraints

In real projects, you rarely get the ideal sample size. Budget limits, tight deadlines, or difficulty finding users often force compromises. Focus on collecting high-quality data from relevant participants rather than chasing large numbers.

Small, well-targeted samples can still reveal critical usability issues and user needs. Use your findings to prioritize improvements and plan follow-up research if needed.