Simple Sample Size Calculator
Quickly compute the sample size needed for a proportion estimate at a chosen confidence level and margin of error.
How to Use the Simple Sample Size Calculator
- Pick confidence.
- Enter expected proportion (50% if unknown).
- Enter margin of error.
- Click Calculate.
Use Cases
- •Quick back-of-envelope survey planning.
- •Teaching inferential statistics.
Formula
n = Z² · p · (1 − p) / E². Pick p = 0.5 for the most conservative estimate.
Frequently Asked Questions
Does this assume simple random sampling?
Yes. Cluster, stratified, or weighted designs need a design-effect adjustment.
Why 50% as default?
p = 0.5 maximises p·(1−p) and yields the largest (safest) sample size when the true proportion is unknown.