SpecWhale

Sample Size Calculator

Estimate sample size for a proportion from confidence z-score and margin of error.

Formula and method

This calculator uses the values you enter and applies the calculation immediately in your browser. The main output formulas are:

  • Sample size: p>1 ? NaN : z*z*p*(1-p)/Math.pow(e/100,2)

Some formulas are undefined for certain input combinations, such as division by zero, equal x-values in a slope calculation, or logarithms of non-positive numbers. In those cases the live tool reports that the result is undefined instead of displaying Infinity or NaN.

Examples

  • Example: with Z-score = 1.96, Expected proportion = 0.5, Margin of error = 5 %, this calculator returns Sample size = 384.
  • Share this page with a clean URL: https://specwhale.com/tools/sample-size-calculator/
  • Try related education & math tools when your next step needs another conversion or calculation.

Embed this tool

Paste this snippet into your own site or blog post to embed a live, working copy of this tool. It links back to the full page on SpecWhale.

Frequently asked questions

Is Sample Size Calculator free to use?

Yes. Sample Size Calculator is completely free, has no usage limit, and does not require an account, email, or API key.

Does Sample Size Calculator store or upload my data?

No. Sample Size Calculator calculates everything locally in your browser. Nothing you type is sent to a server or stored by SpecWhale.

How accurate is Sample Size Calculator?

Sample Size Calculator uses a standard formula (see the Method section above for the exact expression). For high-stakes financial, medical, or legal decisions, confirm the result with a professional or an authoritative source before relying on it.

Can I embed Sample Size Calculator on my own website?

Yes. Use the "Embed this tool" snippet on this page to add a free, working copy of Sample Size Calculator to your own blog post or page.

SEO and sharing notes

This page has a single clean canonical URL, descriptive metadata, breadcrumb structured data, and internal links to related tools. Supported calculators and converters can also copy a prefilled share link without changing the canonical index URL.