Sample Size Calculator
Use the Sample Size to work through sample Size from the values you enter. Review the notes below the result so you understand what the figure represents.
Required sample size
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Without population correction —
Share of population —
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How it works
n = z²·0.25/e², corrected: n/(1 + (n−1)/N)How to use the Sample Size
Enter the requested values and start with one realistic example. Read the result together with its unit or label, then change one input at a time if you want to compare options.
Review the assumptions on the page and confirm any result that affects money, safety, technical work or another important decision.
Frequently Asked Questions
How many people do I need to survey?
For ±5% margin at 95% confidence, about 385 responses regardless of population size; ±3% needs about 1,068. Small populations need fewer thanks to the finite correction.
What do confidence level and margin of error mean?
95% confidence with ±5% margin means: if you repeated the survey many times, 95% of results would land within 5 points of the true population value.
Why doesn't a bigger population need a much bigger sample?
Statistical precision depends on the sample's own size, not the population's — sampling 400 people estimates a city and a country almost equally well once the population is large.