Sample size calculator

How many respondents a proportion survey needs: Cochran's formula with confidence level, margin of error, and optional finite-population correction.

Use 50 when unknown — it gives the largest (safest) n.

n₀ = z²·p(1−p)/e²; with a finite population N: n = n₀ / (1 + (n₀−1)/N).

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How to use

  1. Pick a confidence level.
  2. Enter the margin of error and expected proportion.
  3. Optionally enter the population; read the required n.

What it supports

Cochran's formula (z²·p·(1−p)/e²), n₀ rounded up; finite-population correction n/(1+(n₀−1)/N) applied when a population is given. Proportion defaults to the conservative 0.5. Means, cluster sampling, and nonresponse inflation are not covered.

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