Sample Size Calculator for A/B Testing

Calculate the minimum sample size needed per variation before launching your A/B test, based on your baseline conversion rate and MDE.

Baseline conversion rate

Current conversion rate (%)

%

Enter your current conversion rate. If unknown, use an industry estimate.

Minimum detectable effect (MDE)

Relative lift you want to detect (%)

%

A 10% MDE on a 4% baseline means you want to detect a lift to 4.4% or better.

Test structure

Number of variants (excluding control)

Test type

Two-tailed (detect any change — recommended default) One-tailed (detect improvement only — requires smaller sample)

Test duration estimate (optional)

Average daily visitors to the test page Leave blank to skip duration estimate.