Research Sample Size Calculator (Cochran)
Compute the minimum sample size for a survey using the Cochran formula, with optional finite-population correction.
How to Use the Research Sample Size Calculator (Cochran)
- Pick confidence level.
- Enter expected proportion (50% if unknown).
- Enter target margin of error.
- Enter population size (0 if large or unknown).
- Click Calculate.
Cas d'utilisation
- •Planning surveys.
- •Pilot study sizing.
- •Peer-reviewed research methodology sections.
Formule
n₀ = Z² · p · (1 − p) / E². Finite correction: n = n₀ / (1 + (n₀ − 1) / N).
Questions fréquemment posées
What if I don't know the proportion?
Use 50% — it maximises the variance and therefore yields the most conservative (largest) sample size.
When do I apply the finite correction?
When your population is small (roughly N < 20 × n₀). For very large or unknown populations, leave population at 0 and use n₀.