Why this tool is useful
Create a transparent first estimate for a simple random sample before applying finite-population or design-effect adjustments.
Everyday Calculators · runs locally
Proportion Sample Size Calculator
Estimate an unadjusted sample size for a proportion from confidence z-score, expected proportion and margin of error.
Ready. Your working data stays in this browser.
How it works
It applies n = z² × p(1-p) ÷ e² and reports the unrounded result.
Practical example
At z=1.96, p=50% and margin=5%, the estimate is about 384.16.
Validation
The calculation is deterministic and explains validation errors instead of silently changing invalid input.
Privacy boundary
Input and output remain in this tab. Copy and download happen through browser APIs without a server upload.
Result passport
Every run reports its tool mode, timestamp and input/output size so transformed data can be audited.