Google Ads Statistical Significance Calculator
Test whether your Google Ads A/B test result is statistically significant. Enter visitors and conversions for each variant to see the confidence level.
Free · No signup · Updated June 2026
Your numbers
Results
Estimates for planning only. Your real results depend on audience, creative, and market conditions.
What it measures
Google Ads statistical significance tells you whether the difference between two A/B test variants is real or likely due to random chance, using a z-test on their conversion rates.
Formula
z = (Rate B − Rate A) ÷ Standard error · Confidence from the normal distribution
Worked example
Variant A converts 80 of 2,000 (4%) and Variant B 110 of 2,000 (5.5%), a 37.5% relative uplift with a z-score of about 2.23 and roughly 98.7% confidence.
Typical benchmarks
- Standard threshold
- 95% confidence
- Z-score for 95%
- 1.96
- False-positive risk
- 5% at 95%
How this calculator works
The tool computes each variant's conversion rate, the z-score of the difference, and the resulting confidence level. A confidence of 95% or higher is the usual bar to declare a winner.
Frequently asked questions
What confidence level do I need? +
95% is the standard threshold, meaning there's only a 5% chance the difference is due to randomness.
Why isn't my test significant yet? +
Usually not enough data. Small samples or small differences need more visitors before the result is reliable — let the test keep running.
How large a sample size do I need for an A/B test? +
It depends on your baseline rate and the uplift you want to detect, but reliably catching small differences often requires thousands of visitors per variant.
What is statistical power in A/B testing? +
Power is the probability of detecting a real difference when one exists, commonly targeted at 80%. Low power means a true winner can go undetected.
Can I stop a test as soon as it hits 95%? +
Peeking and stopping early inflates false positives. Set a sample size or runtime in advance and avoid calling the test the moment it briefly crosses the threshold.
Need a custom Google Ads tool, not a generic calculator?
This free google ads statistical significance calculator gets you a number. If you want it wired to your live ad data, GlitchFi builds custom marketing calculators, dashboards, and internal tools, plus full MVPs, with a forward-deployed engineer on your team. Fixed price, 30 days, and you pay nothing if we're late. You own all the code.
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