Sample size calculator
Plan completed responses and invitations for a proportion or mean, with stated confidence, precision and population assumptions.
Normal-approximation precision planning, not a power analysis. Confidence 50–99.99%; finite populations up to one billion. Expected proportions must be strictly between 0 and 100%. A low expected event count triggers a warning. Invitations can exceed the available population and are flagged. Change the input or settings to update your result. Results update as you type. Up to 1,000,000 characters.
Your result
How to use Sample size calculator
- Enter the observations or summary values.
- Choose the method and check its assumptions.
- Review the result and download the calculation.
Useful next steps
Choose the model before reading the result
Plan completed responses and invitations for a proportion or mean, with stated confidence, precision and population assumptions.
Check the assumptions
Normal-approximation precision planning, not a power analysis. Confidence 50–99.99%; finite populations up to one billion. Expected proportions must be strictly between 0 and 100%. A low expected event count triggers a warning. Invitations can exceed the available population and are flagged.
Keep the calculation
Download the JSON for unrounded results and settings, CSV for the table, and the separate assumptions note. The calculation runs in your browser.