About A/B Test Pro
Free, rigorous A/B testing calculators that respect your privacy.
Our mission
Most failed experiments don't fail because of a bad idea. They fail because the test was underpowered, stopped early, or measured the wrong thing. A/B Test Pro exists to make the statistics behind a sound experiment accessible to everyone, without a paywall, a login, or a sales call. Enter your numbers, understand what they mean, and launch with confidence.
What we offer
- A/B Test Sample Size Calculator gives you the required sample size, estimated test duration, and a statistical-power sensitivity table, from your baseline conversion rate and expected lift.
- A/B/C Test Calculator handles three-variant planning with a Bonferroni correction applied across the pairwise comparisons, so the added comparisons don't inflate your false-positive rate.
- Statistical Significance Calculator reports lift, z-score, p-value, confidence, and observed power from your real results.
- In-depth learn guides on sample size, the peeking problem, test direction, and metric design.
How we're built
Statistically rigorous
The calculators use a two-proportion z-test and the standard normal sample-size approximation, with one- and two-sided support throughout. The methods are documented openly in our learn guides and verified against an independent statistical engine.
Private by design
Every calculation runs entirely in your browser. The numbers you type (audience sizes, conversion rates, expected lift) are never sent to our servers, logged, or stored. There is nothing to leak because the data never leaves your device.
Free, with no sign-up
No account, no trial, no credit card. The tools are free to use as often as you like.
Who it's for
Conversion-rate optimization (CRO) specialists, product managers, growth marketers, data analysts, and anyone planning or interpreting an online experiment who wants the math to be right.
Get in touch
Questions, feedback, or a feature request? We'd love to hear from you. Visit our contact page.