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  1. Home
  2. Fake data
  3. A/B test sample size calculator
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A/B test sample size calculator

Enter your baseline rate and minimum detectable effect and get visitors per variant, run-time estimates from daily traffic, and the full formula trace.

This tool is in beta

Still being tested. If a result looks wrong, tell us.

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Enter a baseline and an effect to size the test.

The plan is a normal approximation of the two-proportion comparison, computed before the test runs. Real tests also lose visitors to mid-experiment filtering, cross-device doubles, and peeking at partial results, and those losses push the honest number up. Sequential and Bayesian designs need different sizing than this fixed-horizon plan, and the tool says so rather than pretending to cover them.

Test plan

percent
points
Effect is
Alpha
Power
Test
More settings▾
1 to 20, each compared with the control
Alpha correction
treatment : control
percent in the test
blank or 0 skips the run-time estimate
Formula variant

The baseline sits between 0.01 and 99.99 percent, the allocation ratio between 0.05 and 20, the traffic share between 1 and 100 percent. All numbers stay within ±1,000,000,000,000. A negative MDE plans for a drop.

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