Sample Size Calculator
Work out how many responses you need for a desired margin of error and confidence level — with optional finite population correction.
Required sample size (completed responses)
385
Breakdown
- Size if population infinite
- 385
- Invite at 50% response rate
- 770
- Invite at 25% response rate
- 1,540
Last updated:
FAQ
Why doesn't population size matter much?
Precision depends on absolute sample size, not the fraction sampled — 1,000 responses give ±3% whether the population is a city or a country. Only small populations (under ~50,000) shrink the requirement noticeably.
What margin of error should I aim for?
±5% is the practical standard for most business surveys; ±3% for published polls; anything wider than ±10% usually cannot separate competing options and is only useful for rough exploration.
Why plan for response rates?
The math counts completed responses, but real invitations get ignored. A 25% response rate means inviting four times as many people — the breakdown shows invites needed at typical rates.
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