Your question is Compute A/B Test Sample Size. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
How do you determine the required sample size for an A/B test to achieve statistical significance?
Explain the complete approach rather than naming a calculator. Cover how you would define the primary metric and minimum detectable effect, choose the significance level and statistical power, estimate baseline variance or conversion rate, and translate the result into traffic and test duration. Discuss how the calculation changes for continuous versus binary metrics, unequal allocation, clustering, or a unit of analysis that differs from the randomization unit.
In your response, state assumptions, show a numerical sample-size calculation using clearly labeled illustrative values, and describe how you would pre-register the analysis and validate the result after launch.