Sample Size Per Variant Calculator

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Calculator Configuration

Enter as percentage points (e.g., 0.8 for 0.8% absolute increase)

95%
90%99%
80%
60%95%

Recommended: For a more comprehensive calculator that combines sample size, duration estimation, and comparison tables, check out our Sample Size and Test Duration Calculator.

How it works

Watch a demo of the Sample Size Calculator ⤴

What is Sample Size?

Sample size tells you how many users per variant (control or treatment) are required to detect a given minimum lift with your desired confidence and power.

Calculating Sample Size Given MDE

If you already know your Minimum Detectable Effect (MDE), you can estimate how many users (or samples) you need to start the experiment, per variant.

The Formula

We calculate required sample size using the formula:

n=(Zα+ZβMDE)2⋅2⋅p⋅(1−p)n = \left( \frac{Z_{\alpha} + Z_{\beta}}{\text{MDE}} \right)^2 \cdot 2 \cdot p \cdot (1 - p)

Where:

  • p is the baseline conversion rate
  • MDE is the minimum detectable effect (as a decimal, not a percent)
  • ZαZ_{\alpha} is the Z-score for your confidence level (e.g. 1.96 for 95%)
  • ZβZ_{\beta} is the Z-score for your desired power (e.g. 0.84 for 80%)
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