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Sample Size Calculator
Find the number of survey responses needed for a chosen margin of error and confidence level.
Required sample size
Required sample size: —
Before population correction: —
Critical z value: —
How to use the Sample Size Calculator
- Enter the margin of error you can accept for your survey.
- Set the result you expect and, if you know it, the population size.
- Read the required number of responses in the result panel.
Features
- Required responses for a target margin of error
- Confidence levels of 90, 95 and 99 percent
- Optional finite population correction
- Runs locally, no uploads
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Frequently Asked Questions
Common questions about the free online sample size calculator.
Enter your margin of error, expected result and confidence level, and the calculator returns
the number of responses you need.
At a 95 percent confidence level with no prior estimate, you need about 385 responses for a 5
percent margin of error.
Because the variability of a proportion is largest at 50 percent, so this assumption produces
the safest and largest sample size.
For small populations the required sample is reduced, because sampling a large share of the
population gives more information per response.
Three percent suits most surveys, five percent is common for general research, and one
percent is used for very precise studies.
Only slightly. The required sample grows very slowly with population size, and above a few
thousand it barely changes at all.
No. Always round up to the next whole response, because rounding down would push the margin
of error above your target.
Yes. Enter the population size and the correction reduces the sample, which matters most when
the population is a few thousand or less.
No. Every calculation runs locally in your browser, so your numbers never leave your device.
Yes. It is completely free and unlimited, with no account, no sign-up and no usage limits of
any kind.
Last updated: October 10, 2026