Sample Size Calculator
Find the sample size you need for a survey at 90%, 95% or 99% confidence with a given margin of error. Free statistics tool.
Frequently asked questions
- Why does 50% give the largest sample size?
- p(1−p) is maximized at p=0.5. If you expect a skewed result (say 90% yes), you need fewer respondents for the same margin.
- When does the population size matter?
- Only for small populations. Above roughly 100,000 the finite-population adjustment barely changes the result, so it can be left blank.
- What confidence level should I use?
- 95% is the standard for surveys and academic work. Use 99% for high-stakes decisions, 90% for quick internal polls.
This tool runs entirely in your browser. No data is uploaded anywhere.