A/B Test Sample Size & Significance Calculator
How many users do you need? Is the lift you saw real?
Two modes: sample size (plan the experiment) and significance (read the result). Two-proportion z-test, two-sided, configurable power and confidence.
A 10% MDE on a 5% baseline = detect 5%→5.5%.
Runs entirely in your browser — nothing you enter is sent to a server.
Need this for real, on your stack?
These free tools are a taste of how we think. We’re a senior software team across Romania & Pakistan that ships deep technical work — platforms, infra, data and the gnarly bits in between.
Talk to our engineers →Pick the MDE first
"Minimum detectable effect" is the smallest lift you'd act on. A test sized for a 0.5% lift takes 10× longer than one sized for 2%. Honest MDEs save quarters.
Built by WeWorkWorldwide — a senior software team in Romania & Pakistan that ships deep technical work. Need this turned into something production-grade for your stack? Talk to our engineers →