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A/B Test Sample Size Calculator
Work out how many visitors each variant needs to detect a given lift at 95% confidence and 80% power, and how many days the test will run.
Tip from Tink: Smaller lifts need far more traffic — halve the lift, roughly 4x the visitors.
Visitors per variant
13,911
Total visitors
27,822
Days to run
28
95% confidence, 80% power, two-sided test. Run for at least one full week to cover weekday swings.
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How to use the A/B Test Sample Size Calculator
- Enter your current conversion rate.
- Enter the smallest lift worth detecting.
- Add daily visitors to see test length.
Everything runs in your browser. Nothing you enter is uploaded.