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Sample Size Calculator
Work out how many survey responses you need for reliable results at a chosen confidence level and margin of error.
Sampling Architect
Research Design & Infinite Population Scaling
About the Sample Size Calculator
Work out how many survey responses you need for reliable results at a chosen confidence level and margin of error.
How to use the Sample Size Calculator
- Choose the Confidence Level: 90%, 95% or 99%.
- Enter the Margin of Error (%), the Population Size and the Response Distribution (%) (use 50 if unsure).
- Press Calculate Sample Size.
Formula and method
n₀ = z² × p(1 − p) ÷ e², then adjusted for a finite population: n = n₀ ÷ (1 + (n₀ − 1) ÷ N).
Worked example
At 95% confidence with a 5% margin of error and a very large population, you need about 385 responses.
Tips
- Using 50% for the response distribution gives the safest (largest) sample size.
- Plan for non-responses by inviting more people.
Frequently asked questions
Does a bigger population need a much bigger sample?
No. Beyond a few thousand people, the required sample barely changes.