Math
Sample Size Calculator
Find the sample size needed for a survey given confidence, margin of error, and expected proportion.
Inputs
Sample Size Calculator
Result
Required sample size
385
- Unadjusted n₀
- 385
- z-value
- 1.96
- Population
- Infinite / unknown
How it's calculated
n₀ = z²·p(1−p)/e² · Finite-pop correction: n = n₀ / (1 + (n₀−1)/N).
Common questions
Why default proportion to 50%?
p = 0.5 maximises variance, giving the most conservative (largest) sample size when the true proportion is unknown.
When do I need the finite population correction?
When the sample is a meaningful fraction of the total population (roughly >5%).
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