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A/B Test Sample Size Calculator — Free, Two-Proportion Z-Test

Free A/B test sample-size calculator using the two-proportion z-test. Set baseline CVR, MDE, and confidence level — get the per-variant sample size needed.

A/B Test Sample Size Calculator

Per variant

31,196

Total (A + B)

62,392

Target new rate

5.50%

Assumes 80% statistical power. Smaller minimum-detectable-effect (MDE) = much larger sample. Detecting a 5% lift on a 2% baseline takes ~30K visitors per variant.

About this tool

Why undersized A/B tests waste time

Calling a winner before reaching statistical significance is the most common A/B-testing mistake. A 5% lift on a 2% baseline needs ~30K visitors per variant at 95% confidence. Smaller minimum detectable effects = much larger samples.

How to use the A/B Test Sample Size Calculator

Takes about a minute. No signup, no download, your data stays in your browser.

  1. 1
    Open the tool. Scroll up to the A/B Test Sample Size Calculator above — it loads instantly in your browser, no install needed.
  2. 2
    Enter your values. The fields come pre-filled with realistic defaults so you can see how it works — replace them with your own numbers.
  3. 3
    Read the result. The output updates instantly. Copy or share it — nothing is uploaded to a server, everything stays on your device.

Frequently asked questions

Common questions about the A/B Test Sample Size Calculator.

Is the A/B Test Sample Size Calculator free to use?

Yes. The A/B Test Sample Size Calculatoron 7BusyBoss is completely free — no signup, no paywall, no usage cap.

Do I need to sign up to use the A/B Test Sample Size Calculator?

No. The A/B Test Sample Size Calculatorworks instantly in your browser — no account needed. Signing in with Google is optional and only unlocks features like saving favorites and higher AI build limits.

Does the A/B Test Sample Size Calculator work on mobile?

Yes. Every tool on 7BusyBoss is mobile-responsive and works in any modern browser — Chrome, Safari, Firefox, Edge — on phones, tablets and desktops.

Is my data safe when I use the A/B Test Sample Size Calculator?

Yes. The A/B Test Sample Size Calculatorruns entirely in your browser — your inputs never leave your device unless the tool explicitly fetches public data (e.g. currency rates). We don't store the values you type.

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