Sample Size Calculator
Estimate required sample size from confidence level, margin error, and proportion.
Sample Size Calculator estimates how many observations are needed to measure a proportion with a chosen confidence level and margin of error. Confidence level controls how much uncertainty the interval allows, margin of error is the maximum acceptable distance between the estimate and the true population value, and estimated proportion is the expected share of responses or outcomes. The most conservative proportion is often 50%, because it produces the largest required sample when the true proportion is unknown. Population size matters mainly for smaller finite populations; for very large populations the finite correction becomes negligible. This calculator is useful for surveys and experiments, but representativeness, nonresponse, selection bias, and measurement quality are just as important as the numeric sample size.