Sample Size Calculator
Computes the minimum sample size needed to estimate a population proportion within a specified margin of error, at a chosen confidence level, using the standard formula n = z²p(1-p)/e². If a finite population size is provided, applies the finite population correction to reduce the required sample size accordingly.
Choosing a sample size before running a survey or experiment is a common statistics task — too small a sample and your results are too noisy to trust; too large and you waste time and budget collecting unnecessary data. This calculator applies the standard formula used in survey methodology and A/B testing so you don't have to derive it by hand.
Typical use cases: sizing a customer survey before fielding it, planning a poll with a target margin of error, or determining how many users an A/B test needs per variant.
Adjust confidence level, margin of error, and estimated proportion to see how each affects the required sample size in real time.