🔬 Statistics Calculator

Sample Size Calculator

Determine the minimum sample size needed for statistical surveys and experiments — for proportions and means — at your desired confidence level and margin of error.

Sample Size Parameters

Confidence Level

Margin of Error (e)

% (proportion)

Estimated proportion (p) — use 0.5 if unknown

Population size (N) — leave blank for infinite

Enter parameters above

Proportion: n = z²pq/e² · Mean: n = (zσ/e)²

Quick Reference (Proportion, p=0.5)

Margin of Error	90% CI	95% CI
±10%	68	97
±5%	271	385
±3%	752	1068
±1%	6766	9604
±0.5%	27059	38416

Frequently Asked Questions

What sample size do I need for a poll?

For a national poll with ±5% margin of error at 95% confidence, you need n≈385 (assuming p=0.5). Most news polls use 1,000–1,500 respondents giving ±3% error.

What is finite population correction (FPC)?

When your population is small, the FPC reduces required sample size: n_corrected = n / (1 + (n-1)/N). This gives credit for surveying a substantial fraction of the total population.