Free Tool
Sample Size Calculator: How Many Responses Do You Need?
Determine how many survey responses you need for statistically valid results. Our sample size calculator helps you plan surveys with the right level of precision.
How This Calculator Works
The sample size calculator uses your desired margin of error, confidence level, and population size to determine how many responses you need. Larger samples give more precise results but cost more to collect.
The Formula
n = (Z² × p × (1-p)) / E² for infinite populations, adjusted by n × N / (n + N - 1) for finite populations. Where Z is the z-score for your confidence level, p is expected proportion (typically 0.5), and E is margin of error.
How to Interpret Your Results
The calculated sample size tells you the minimum number of completed responses needed. If your expected response rate is less than 100%, divide by your response rate to determine how many invitations to send.
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Numbers are useful, but predicted market data is better. Validate your idea with 500+ data points in about 1 hour.
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95% is standard for most research. Use 99% for critical decisions, 90% for directional insights.
Plus or minus 5% is common for general research. Plus or minus 3% for higher precision. Plus or minus 10% for rough estimates.
Only for small populations (under 10,000). For larger populations, sample size depends mainly on desired precision, not population size.
Using 50% gives the maximum required sample size, ensuring your sample is large enough regardless of actual results.