Sample Size Calculator
How many survey responses you need for a target margin of error.
Enter values
%
—
—
Step by step
The formula
n₀ = z² · 0.25 / e² (with finite-population correction when N is known)
All calculations run locally in your browser and update instantly as you type.
Related calculators
Frequently asked questions
Why does it assume a 50% proportion?+
A proportion of 0.5 maximises variance, giving the largest (safest) sample size. If you know the real proportion is far from 50%, you can survey slightly fewer people.
All calculations run locally in your browser. Nothing you type is sent to a server.