Sample Size Calculator

Find how many responses you need for a survey to hit a target margin of error.

Use 50% if unsure; it gives the largest (safest) size.
Fractions and decimals both work.
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Sample size
For a very large population
Critical value (z)
If 30% respond, invite
Work

Saved Calculations

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How to Calculate Sample Size

n₀ = z² × p(1 − p) ÷ e²   With a population N: n = n₀ ÷ (1 + (n₀ − 1) ÷ N)

Round up to the next whole response.

Worked Example

Tips

This assumes a simple random sample. Halving the margin of error needs about four times as many responses. The margin of error calculator works the other way, from a sample size you already have.