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HomeFree ToolsSurvey Sample Size Calculator
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Survey Sample Size Calculator

Tells you how many responses you need for results to be statistically meaningful. Uses the standard Cochran formula with finite-population correction.

Frequently asked questions

What confidence level should I pick?

95% is standard for most product and customer research. 99% if the decision is high-stakes (medical, legal).

What margin of error should I aim for?

5% is the default. Tighter (3%) needs roughly 2.7× more responses. Looser (10%) cuts the required sample by ~75%.

What if I don't know the total population?

Use 100,000 or higher — the required sample size barely changes once the population is large.

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LemForms is the form builder this tool plugs into — calculations, conditional logic, embeds, webhooks, and a real submissions dashboard. Free to start.

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Required sample size
383
responses for 95% confidence ± 5% margin
Uses the Cochran formula with finite-population correction. Assumes worst-case 50/50 response split.