How to use it
- Choose a 90%, 95%, or 99% confidence level.
- Enter the margin of error and expected proportion as percentages.
- Optionally enter a finite population size, then calculate the required response count.
Sample Size Calculator
Estimate how many responses a proportion-based survey may require.
About the Sample Size Calculator
This calculator estimates a starting survey sample size for measuring a population proportion under common confidence levels.
Calculation logic
The initial estimate uses n = z squared times p times (1 - p), divided by the squared margin of error. A finite population correction is applied when population size is provided.
Choosing the proportion
When no prior estimate is available, 50% is conservative because it produces the largest required sample under the proportion formula.
Planning note
The result estimates completed responses, not invitations. Real surveys may need a larger outreach pool to account for nonresponse and sampling design.