Calculate the minimum sample size needed for a survey or study, based on confidence level, margin of error, and population size.
This tool determines how many respondents or data points you need to survey or measure to achieve a statistically reliable result.
Sample size equals Z squared times p times (1-p), divided by the margin of error squared, with an optional finite population correction.
Select your confidence level, enter your desired margin of error and estimated population proportion, and optionally the total population size, then click Calculate.
Example: For a 95% confidence level, 5% margin of error, and 50% proportion, you need approximately 385 respondents for an infinite population.
What proportion should I use if unsure. Use 50%, since it produces the most conservative (largest) sample size requirement.
Why does population size matter. For smaller finite populations, the required sample size can be reduced using a finite population correction factor.