Sample Size Calculator
Work out how many visitors your test needs before you launch it, so you know whether it's worth running.
How the calculator works
It uses a standard sample size formula for comparing two proportions. The smallest lift is relative, so a 20% lift on a 5% conversion rate means reaching 6%.
Testing several variants divides your significance level between them with a Bonferroni correction, so each group needs more visitors.
How to choose your inputs
Smaller lifts take far more visitors to detect, so set the smallest lift that would actually change your decision. If the sample is out of reach, test a bolder change or a higher-traffic page.
Power is the chance of detecting a real effect of that size, and 80% is a common choice. Add your visitors per day for a rough timeline, then run the test through full business cycles even if you reach the number sooner.
Disclaimer
This tool is for informational purposes only, and we don't guarantee the accuracy of its results. You're responsible for verifying any results before relying on them. See our terms of use.
Common questions
Is my information saved?
No. Your numbers stay in your browser, and they aren't sent to anyone.
What if I don't have enough traffic?
Test a bigger change, use a page or a conversion step with more volume, or accept a lower confidence level knowing it raises the risk of a false win.
Can I stop a test once it looks like a winner?
It's best not to. Checking early and stopping at the first good reading raises your chance of a false win, so reach your planned sample first.
How do I check the result when the test ends?
Enter your visitors and conversions in the A/B Test Calculator to see whether the result is statistically significant.
Try the A/B Test CalculatorWant help putting this to work?
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