How do I calculate sample size? Enter your numbers above and the result updates instantly. For example: Population size (0 = unlimited): 10,000 · Confidence level: 95 · Margin of error: 5% → Required sample size: 370.
Is this Sample Size Calculator free? Yes — completely free with no sign-up or paywall. It runs entirely in your browser and keeps working offline; the numbers you enter never leave your device.
How accurate is it? It uses the standard published formula for sample size. Results are estimates for planning — not financial, tax, medical, engineering, or legal advice.