Sample Size Calculator
Find the survey sample size for your margin of error.
Sample size needed
370
Infinite-population size
385
Share of population
3.7%
Assumes maximum variance (p = 0.5), the conservative standard for surveys.
Precision is expensive
Halving the margin of error quadruples the required sample — the formula divides by e². A ±5% national poll needs ~384 responses; ±2.5% needs ~1,537. Population size barely matters once it's large, which is why 1,000 people can represent a country.
Sampling beats volume
The math assumes random sampling; a million self-selected online votes carry more bias than 400 random ones. Budget survey effort for response quality and randomness first — the sample-size formula can't rescue a skewed frame.
Frequently asked questions
- How does the Sample Size Calculator work?
- Find the survey sample size for your margin of error.
- Is the Sample Size Calculator free to use?
- Yes. The Sample Size Calculator is completely free, runs entirely in your browser, and requires no account or sign-up. Your inputs never leave your device.
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