Free tool
Sample Size Calculator — plan honest experiments.
Enter your confidence level, margin of error, and population proportion. Get the sample size you need to make a defensible decision.
How confident the estimate falls within your margin
Your acceptable +/- around the estimate
±5%
If unknown, leave at 50% — the most conservative choice
50%
Optional — for finite populations (e.g. employee surveys)
Tip: If you don't know your population proportion, use 50%. It produces the largest sample size — the safest assumption.
Required sample size
385
responses needed
Unadjusted
385
Z-score
1.960
Formula: n = (z² × p × (1 − p)) / e², adjusted for finite population when set.
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