Sample Size Calculator

How this is calculated

This tool uses Cochran's formula for estimating a sample size for proportions:

n₀ = (Z² × p × (1−p)) / e²

Where Z is the Z-score for your chosen confidence level, p is the expected proportion (use 50% if unknown — it gives the most conservative, largest estimate), and e is your acceptable margin of error. If you provide a population size, the finite population correction is applied: n = n₀ / (1 + (n₀−1)/N).

This calculator estimates sample size for a single proportion. Studies with more complex designs (e.g., comparing two groups, survival analysis, cluster designs) need a different formula — get in touch if you'd like help with power analysis for a specific design.