Workflow tool

Sample Size Calculator

Calculate the minimum sample size for your study. Choose the design that matches your study and fill in your parameters. Calculation steps are shown so you can document the approach in your protocol.

Templates are guidance tools. Discuss your sample size with your supervisor or methods advisor before finalising.

Required inputs

Expected prevalence or proportion (p)Use 0.5 if unknown — this gives the largest sample

Acceptable margin of error (e)0.05 = ±5 percentage points

Confidence level

Optional adjustments

Leave blank if not applicable.

Total population size (N)Only needed if population is small (<10,000)

Expected response rate0.9 = 90% — adjust sample up for non-response

Design effect (DEFF)1 = simple random sample. Use 1.5–2.5 for cluster sampling

Minimum sample size

428

participants required

Raw Cochran result: 385 → after response rate adjustment: 428

Calculation steps

1.Basic Cochran formula
n = Z² × p × (1-p) / e²
= 1.960² × 0.5 × 0.50 / 0.05² = 385
2.Non-response adjustment (response rate = 90%)
n_final = n / response_rate
= 385 / 0.9 = 428

Formula: Cochran (1977) — n = Z²p(1-p)/e² — a standard formula for estimating sample sizes in cross-sectional surveys. Adjust p toward 0.5 if uncertain about prevalence; this gives the most conservative (largest) estimate.

Important: This calculator gives a minimum sample size based on statistical requirements. In practice, add 10–20% for anticipated dropouts, missed interviews, or data quality issues. Always discuss your sample size approach with your supervisor or methods advisor before finalising.