How it works
p1 = baseline; p2 = p1 × (1 + MDE). n = ceiling([zα√(2p̄(1−p̄)) + zβ√(p1(1−p1)+p2(1−p2))]² ÷ (p2−p1)²).
ASO and experiments
A/B test sample size calculator
Plan a per-variant sample to compare two conversion rates with equal allocation, a two-sided test, and a normal approximation.
- Sample per variant
- 8,158
- Total sample (two variants)
- 16,316
- Minimum detectable conversion
- 6%
Estimate without continuity correction. Requires independent observations, two variants, and equal allocation; not for sequential tests or multiple comparisons.
Worked example
A 5% baseline, 20% relative MDE, 95% confidence and 80% power plan about 8.2k observations per variant.
Assumptions and limits
Estimate without continuity correction. Requires independent observations, two variants, and equal allocation; not for sequential tests or multiple comparisons.
Method reference: NIST: difference of proportions
Frequently asked questions
How do I use the a/b test sample size calculator?
Plan a per-variant sample to compare two conversion rates with equal allocation, a two-sided test, and a normal approximation.
Does a 20% MDE mean 20 percentage points?
No. With a 5% baseline, 20% relative lift means reaching 6%, a difference of 1 percentage point.
Do I need an account and are my inputs uploaded?
No account is required. Calculations run in your browser. Entered numbers and text are not included in tool analytics events; only the tool ID, language, and action are recorded.
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