Sample Size Calculator
Find how many survey responses you need for a chosen margin of error. The result updates as you type, with the working underneath so you can check it.
Your details
Result
Sample size needed
385
- Without population correction
- 385
- Critical z
- 1.960
Good to know: n = z² p(1−p) ÷ e²
About this tool
Formula
n = z² p(1−p) ÷ e²
Questions people ask
Why use 50% as the expected proportion?
It gives the largest sample size, so it is the safe choice when you don't know the true proportion.
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How we calculate this
We use the standard published formula or definition for this calculation, and we show the working so you can check it.
Spotted a mistake? Tell us and we'll check it. How we check our calculators