Sample Size for a Proportion

How many respondents do you need for a given margin of error?

Margin (e.g. 0.05 = 5%) Proportion (p) Confidence

Enter values above, or load an example.

About this tool

Computes n = z²·p·(1−p)/m². Pick your margin and confidence; defaults to p=0.5 (worst case) and 95% confidence.