How this calculator works
Enter baseline success rate (%), desired margin of error (%), z score. Select Calculate to apply the displayed formula and review the labeled results.
Formula / method
n = z² × p(1 − p) ÷ margin²
Worked example
An 80% baseline, 3% margin and 95% z score needs about 683 examples.
Assumptions and limitations
Examples are independent and the normal proportion approximation is appropriate.
This is not a power analysis for A/B comparisons and does not correct for stratification or multiple tests.