Find the sample size needed to estimate a proportion at a chosen confidence and margin of error. Pick the confidence and enter the margin.
Sample Size
— responses
Needed for the survey.Usage Tip
Halving the margin of error quadruples the required sample size — precision gets expensive fast.
THE MATH
n = z² × p(1 − p) ÷ E²
z from the confidence level, E the margin of error
z from the confidence level, E the margin of error
This gives the number of responses needed for a survey to hit a target margin of error.
A proportion of 50 percent is the most conservative (largest) sample requirement.
A proportion of 50 percent is the most conservative (largest) sample requirement.
Choose the confidence level and enter the margin of error as a percent.
The expected proportion defaults to 50 percent (worst case).
The result is rounded up to a whole number of responses.
The expected proportion defaults to 50 percent (worst case).
The result is rounded up to a whole number of responses.