Sample Size Calculator
Calculate the sample size needed for a survey or study using Cochran's formula with finite-population correction.
N
%
Result
Required Sample Size
370
What is a sample size calculator?
A sample size calculator tells you how many responses you need for a survey or study to be statistically reliable. It uses Cochran's formula and applies a finite-population correction so the result stays sensible for smaller populations.
Formula
n = n₀ ÷ (1 + (n₀−1)/N) [finite-population correction]
Example
For a population of 10,000 at 95% confidence and a 5% margin of error, you need about 370 respondents. Narrower margins or higher confidence increase the required sample.
Common Use Cases
- Planning market-research and customer surveys.
- Sizing clinical or academic studies.
- Estimating poll respondent counts.
FAQs
Why is p set to 0.5?
p = 0.5 maximizes p(1−p), giving the most conservative (largest) sample size — safest when you don't know the expected proportion.
What does the finite-population correction do?
For small populations it reduces the required sample below the infinite-population estimate, since you're sampling a meaningful fraction of the whole group.