Sample Size Calculator

Formula

z²p(1−p)/e²

Worked example

p=.5,e=.05 — 385

Quick answer

What does the Sample Size Calculator do?

Estimate sample size for a proportion at 95% confidence.

What is the Sample Size Calculator?

Estimate sample size for a proportion at 95% confidence. Use it when you have the required inputs and want a deterministic, repeatable result with the calculation method visible.

How to use this calculator

Enter the values requested by the tool, keep units and time periods consistent, resolve any validation message, calculate, then review the primary answer together with the displayed formula and supporting values.

Formula and method

This calculator uses the deterministic formula z²p(1−p)/e². Enter the required values, then review the displayed substitution and result breakdown to verify the calculation.

Worked example

p=.5,e=.05 385

Common mistakes to avoid

Check units, decimal points, percentages, signs, date/time order, selector choices, and rounding. For important decisions, verify the result against an independent source or qualified professional when appropriate.