Sample size for a proportion
Sample size for a proportion: calculate a transparent estimate from the values and assumptions you provide.
Your inputs stay in your browser. Displayed results are rounded to a maximum of 12 significant digits.
Method and assumptions
Method version 1.0.0 · Updated
Calculate
Formula: n = z² p(1−p) / e², rounded up
Sample size for a proportion: calculate a transparent estimate from the values and assumptions you provide.
- zScore
- Z value for confidence level
- marginPercent
- Desired margin of error (%)
- expectedProportion
- Expected proportion (%)
Simple random-sample approximation; excludes finite-population and non-response adjustments.
Calculate with code
These short examples use the same inputs and core calculation as this tool. Adapt validation and formatting to your application.
JavaScript
const n = Math.ceil(1.96 ** 2 * 0.5 * 0.5 / 0.05 ** 2); // 385