Pre-Test Planning

Sample Size Calculator

Don't start a test without a plan. Calculate exactly how many visitors you need to reach statistical significance.

Your current conversion rate before testing.

The smallest lift you care about detecting (e.g. 10%). Smaller MDE = Much more traffic needed.

Likelihood of finding a winner if one exists. Standard is 80%.

Used to estimate the duration in days.

Required Sample Size
0
Visitors per variation
Est. Duration (Standard) 0 Days
With Zyro (Sequential) 0 Days
Zyro's Sequential Testing lets you peek early and finish up to 50% faster than fixed-horizon tests.
Test Faster with Zyro

Why Sample Size Matters

If you stop a test too early, you risk a "False Positive" (thinking a variation is a winner when it's actually random noise). If you run it too long, you waste traffic on a losing variation.

This calculator uses the standard Frequentist formula to determine the "Fixed Horizon" sample size. This means you must commit to this number of visitors before you look at the results.

The "Fixed Horizon" Problem

Traditional A/B testing is rigid. If you see a winner on Day 3, you are technically not allowed to stop until Day 20 (based on the calculator). This wastes money.

Zyro uses Sequential Bayesian Statistics. This modern approach allows you to check results daily and stop as soon as a winner is statistically proven, often cutting test duration by half.