Sample Size Calculator: One Proportion

Sample size to estimate a single proportion within a target margin of error, with design-effect and response-rate adjustment.

Population size N

Target margin of error

Confidence level

Expected proportion p

Design effect

Expected response rate

Calculating…

Required sample draws vs. target margin of error. Tighter targets explode the required n; the marker shows your target.

Assumption check

For surveys estimating one percentage (support, incidence, prevalence). Uses Cochran’s formula with the finite population correction.

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