Why is a sample size calculator useful for A/B testing?

• A. It predicts revenue
• B. It helps determine the required sample size and test duration based on daily visitors and the number of variations
• C. It ensures a 100% confident result
• D. It estimates the best performing variant

Answer: (B)

A sample size calculator is useful in A/B testing because it helps you plan how much data you need and how long the test should run to reliably detect a meaningful difference between variants. By inputting your daily visitors, the number of variations, and choices like the desired statistical significance and power, the calculator estimates the required sample size per variant and an approximate test duration. This makes it easier to set realistic timelines and allocate traffic so the test yields trustworthy results.

It’s essential because running a test with too little data can lead to inconclusive or misleading conclusions, while too much data wastes time and resources. The calculator helps you account for multiple variants and the expected effect size, ensuring you collect enough observations to confidently detect real differences rather than random noise. It’s a planning aid that informs how long you need to run the test based on traffic and variation count.

This tool doesn’t predict revenue, guarantee a 100% confident result, or automatically tell you which variant will win. It’s about sizing and timing to achieve reliable statistical power, given your traffic and test setup.