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About the Sample Size Calculator
This calculator computes the minimum sample size you need for a survey or study. Enter your confidence level and margin of error, and it returns the number of respondents required for statistically valid results.
The tool applies the standard Cochran formula n = z² × p × (1 − p) / e², where z is the z-score for your confidence level, p is the expected proportion, and e is the margin of error. When you enter a population size, it also applies the finite population correction. Key inputs are confidence level, margin of error, expected proportion, and population size. If you do not know the expected proportion, use 0.5, since it gives the largest, most conservative sample size.
- Choose a confidence level, such as 90%, 95%, or 99%.
- Enter your margin of error, commonly 5% or 3%.
- Add your population size if known, then read the required sample size.