How it works
n₀=z²p(1−p)/e²; for finite N, n=n₀/[1+(n₀−1)/N]; round sample size upward.
Input definitions
- Expected proportion (%)
- Enter the value in the labeled unit.
- Desired margin (percentage points)
- Enter the value in the labeled unit.
- Two-sided confidence
- Choose 90% / 95% / 99%.
- Finite population (0 = large/unknown)
- Enter the value in the labeled unit.
A worked example
- Expected proportion (%)
- 50
- Desired margin (percentage points)
- 5
- Two-sided confidence
- 95%
- Finite population (0 = large/unknown)
- 0
Assumptions & limits
Planning approximation for proportions, not a confidence interval for observed data. Extreme proportions and small samples may need exact methods; finite-population correction assumes sampling without replacement. Required sample sizes above one billion are rejected.
Sources & review
Maintained by AnsRio. Methods and examples use automated checks; this does not imply independent professional certification.
Method updated 2026-10-17. Content checked against the stated method and examples. Our verification approach.
Common questions
Why can statistical results differ between tools?
Denominator, interpolation and boundary conventions can differ. Use the method and assumptions on this page to compare the same definition; displayed decimals may also be rounded.
How does the Survey sample size for a proportion tool work?
n₀=z²p(1−p)/e²; for finite N, n=n₀/[1+(n₀−1)/N]; round sample size upward.
What are the assumptions and limits of Survey sample size for a proportion?
Planning approximation for proportions, not a confidence interval for observed data. Extreme proportions and small samples may need exact methods; finite-population correction assumes sampling without replacement. Required sample sizes above one billion are rejected.