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Statistics Calculators
Sample Size Calculator
Calculate the minimum sample size needed for a survey to achieve a target margin of error at a given confidence level.
Required sample size
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About the Sample Size Calculator
This calculator determines the minimum number of survey respondents needed to estimate a population proportion within a desired margin of error, at a chosen confidence level.
Formula: n = (z² × p(1 − p)) ÷ e², using z = 1.645 (90%), 1.96 (95%) or 2.576 (99%), and e as the margin of error (decimal)
Using 50% for the expected proportion is the most conservative choice when the true proportion is unknown, since it maximizes the required sample size. Tighter margins of error and higher confidence levels both require larger samples.
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