Question 1

How do I calculate sample size for an A/B test?

Accepted Answer

Sample size depends on your baseline conversion rate, minimum detectable effect (MDE), statistical power (typically 80%), and significance level (typically 95%). Use our calculator to input these values and get an exact sample size requirement.

Question 2

What is minimum detectable effect (MDE)?

Accepted Answer

MDE is the smallest improvement you want to detect. For example, if your conversion rate is 2% and you set MDE to 15%, you want to detect improvements to 2.3% or higher. Typical MDE values are 10-20%. Lower MDE requires larger sample sizes.

Question 3

How long should I run my A/B test?

Accepted Answer

Run tests for at least 1-2 weeks minimum to account for day-of-week effects, and until you reach your predetermined sample size. Never stop early just because you see 95% confidence. Our calculator estimates test duration based on your daily traffic.

Question 4

What is statistical power in A/B testing?

Accepted Answer

Statistical power is your ability to detect a real effect when one exists. 80% power (industry standard) means you will catch a real improvement 80% of the time. Higher power requires more visitors but reduces false negatives.

Input Parameter	Value
Daily Visitors Average daily traffic to your test page	1,000
Baseline Conversion Rate Your current conversion rate	2.0%
Minimum Detectable Effect (MDE) Relative improvement you want to detect (10-20% typical)	15%
Statistical Power Ability to detect real effects (80% is standard)	80%
Significance Level Confidence level (95% is standard)	95%

A/B Test Sample Size Calculator

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Best Practices for Ecommerce A/B Tests