Proportion sample size
Estimate a survey sample size for a target margin of error.
How this works
n = ceiling[z²p(1−p)/E²]. Use p = 0.5 when uncertain.
Example
Using the example inputs, minimum sample size is 385.
- Expected proportion (0–1)
- 0.5
- Margin of error (0–1)
- 0.05
- Critical z value
- 1.96
- Minimum sample size
- 385
Scope and assumptions
Large-population normal approximation; does not adjust for nonresponse, clustering, or finite populations.
NIST statistical methods handbook