Marketing & Email calculator
A/B Test Sample Size
Plan an A/B test properly: find how much traffic you need to detect the improvement you care about. Everything runs in your browser — nothing you enter is sent anywhere.
Your numbers
Change any value — results update as you type
Values are estimates. Nothing you enter leaves this page.
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Total visitors needed
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Estimated test duration
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Rate you are trying to detect
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Read this estimate carefully
Estimate for a two-sided test of two proportions. Run the test for full weeks and do not stop it early when it first looks significant.
How to use it
- Enter your current conversion rate.
- Enter the smallest relative improvement worth detecting.
- Keep 95% confidence and 80% power unless you have reasons to change.
- Add daily test traffic to estimate duration.
How it is calculated
- Target rate = baseline × (1 + improvement)
- n = (z(α/2)·√(2p̄(1−p̄)) + z(β)·√(p₁(1−p₁)+p₂(1−p₂)))² ÷ (p₂−p₁)²
- Duration = 2 × n ÷ daily visitors
Common questions
Why so many visitors?
Small differences are hard to tell from chance, so you need a lot of data.
Can I stop early?
Stopping when results first look good inflates false positives.
What if I do not have enough traffic?
Test bigger changes, or use a higher-traffic page.