Sample Size Calculator
Find the sample size needed to estimate a population proportion at a given confidence level and margin of error.
Input Data
例如 5 表示 ±5%。
預期占比 (0–1)，預設 0.5 最保守。
設 0 表示母體極大，不修正。
Results
385
n ≈ 385 (95% CI, ±5%)
At a glance:To estimate a population proportion p, the required sample size depends on the z for the confidence level, the margin e and the expected proportion p: n₀ = z²·p(1−p)/e². For a finite population N, multiply by the finite-population correction.
Formula
n₀ = z²·p(1−p)/e².
Finite: n = n₀ / (1 + (n₀−1)/N).
How to Use
- Pick a confidence level.
- Set margin and expected proportion.
- Optionally enter population size for correction.
FAQ
Why use p = 0.5?
p=0.5 maximizes p(1−p), giving the most conservative (largest) sample size, safe for any scenario.
Very large population?
With a huge population the correction factor approaches 1, so n₀ alone suffices.
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References
Content review: Calculatorism Science Team. Results are for reference only.