# Sample Size Calculator

> Sample size calculator: determine how many survey respondents you need for a target confidence level and margin of error. Free, no signup, runs in your browser.

- **Canonical URL:** https://boringtoolskit.com/sample-size-calculator/
- **Category:** Everyday Calculators
- **Evidence level:** authored-methodology
- **Reviewed:** August 2026
- **Last verified:** 2026-10-12
- **Privacy:** Inputs and results stay in this browser unless the page clearly labels an external request.

## How it works

n = z^2 x p x (1 - p) / margin^2, with z = 1.96 at 95% confidence and p = 0.5 the conservative proportion.

## Worked example

A survey with +/-5% margin at 95% confidence needs 385 respondents.

## Sources

- [Calculation methodology and verification standard](/methodology/)

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