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A/B Test Sample Size Calculator

Compute the sample size and test duration needed for a statistically valid A/B test.

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Open A/B Test Sample Size Calculator and you get an answer straight away, with no account to create. You will find it under Conversion & analytics, with Social Media Image Size Guide and Bounce rate calculator for the neighbouring cases.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is A/B Test Sample Size Calculator?

Compute the sample size and test duration needed for a statistically valid A/B test.

When would I actually use this?

Finding where a journey leaks: which step loses the most people relative to its own traffic, what fixing it would be worth, and how many visitors a test needs before its result means anything.

What is the most common mistake?

Fixing the step that loses the most people. That is almost always the first one, simply because everybody starts there — the weak step is the one with the worst rate relative to the traffic reaching it.

How is A/B Test Sample Size Calculator different from Social Media Image Size Guide?

They sit next to each other but answer different questions: Social Media Image Size Guide is the one to open when you need it to recommended image dimensions for Instagram, Facebook, X, YouTube, TikTok, LinkedIn and Pinterest, each flagged as documented by the platform or as a usage convention — plus a checker that tells you what your own image loses to the crop. Pick whichever matches what you're starting from — both are free.

Where do the figures come from?

The maths is exact for the counts you enter, and it assumes each step is measured over the same period and the same population. Sample-size guidance follows the standard test for two proportions.

Further reading

All guides →
GuideHow Many Visitors Does an A/B Test Need?Sample size is set by your baseline conversion rate and the relative lift you want to detect — and it explodes as that lift shrinks. Here is the formula, a full table at a 3% baseline, and why stopping early breaks the test.ExplainerBounce Rate Is Not What Most People Think It IsA bounce was never a measure of dissatisfaction — it was a session that sent one hit. Google Analytics 4 replaced the definition entirely, and the new one is a configurable timer. Here is the same thousand sessions read five ways.ExplainerWhen to Post, and Why the Answer Is Mostly Not the TimePublished best-time tables average over audiences that are not yours, and on a ranked feed posting time matters far less than it did on a chronological one. Compute your own audience's activity across time zones instead — six zones flatten the timing lever from a 94% swing to a 22% one — and see how many posts a real timing test needs.ExplainerCost Per Click, and What You Are Actually Bidding AgainstYour bid decides whether you are eligible; the advertiser below you decides what you pay. Doubling a bid can move the price not at all, quality can halve it for the same position, and the average CPC in your report is a click-weighted mixture that describes no query. The auction arithmetic, worked.ExplainerCart Abandonment: The Metric and the Money Behind ItAbandonment rate is one minus completed over created — and the figure quoted everywhere is an average across wildly different shops. The useful work is turning a percentage point of checkout completion into money, then discounting it for returns.ExplainerWhat Is a Conversion Rate? Conversions Divided by Visitors Times 100, With BenchmarksA conversion rate is the share of visitors who take a desired action. Here is the simple formula, typical benchmarks, and how to read the number without fooling yourself.