📋 Sample Size Calculator

±%
%
Use 50% if unsure – it gives the largest, safest sample.
Optional – leave blank for a large or unknown population.

Required sample size

385

responses for ±5% at 95% confidence

z-score
1.96
Without population correction
385

Step by step

  1. z-score for 95% confidence: z = 1.96
  2. n₀ = z² × p(1 − p) ÷ e² = 1.96² × 0.5 × 0.5 ÷ 0.05² = 384.15
  3. Round up to a whole number of responses: n = 385

If you expect only part of the people you contact to respond, divide by the response rate – e.g. 385 ÷ 0.3 = 1,284 invitations at a 30% response rate.

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