SEO & Marketing
A/B Test Sample Size Calculator
The A/B Test Sample Size Calculator estimates how many visitors each variant of a test needs before you can trust the results, based on your baseline conversion rate and the smallest effect you want to detect.
Enter your numbers and get a quick estimate of visitors per variant -- calculated instantly using a standard rule-of-thumb formula.
How to Use the A/B Test Sample Size Calculator
- Open the A/B Test Sample Size Calculator.
- Enter your baseline conversion rate.
- Enter the minimum detectable effect you want to catch.
- Read the estimated visitors needed per variant and in total.
Frequently Asked Questions
What is a minimum detectable effect?
It's the smallest change in conversion rate you want your test to reliably detect -- a smaller effect requires a larger sample size to detect confidently.
What confidence level does this assume?
This estimate uses a common rule-of-thumb formula targeting roughly 95% statistical significance and 80% power.
Is this exact enough for a rigorous experiment?
It's a solid quick estimate for planning purposes -- for a rigorous, formal experiment, confirm with a dedicated statistics tool or consult a statistician.