Sample Size Calculator
How many responses does a survey need? Compute the sample size from margin of error and confidence level.
About the Sample Size Calculator
For an infinite population: n = z² × p(1−p) / e², with z from the confidence level (1.645 for 90%, 1.96 for 95%, 2.576 for 99%) and p the expected proportion (use 50% when unknown, it is the conservative choice). Finite populations apply the correction n/(1+(n−1)/N).