Sample Size Calculator  ChiSquared Test  Sequential Sampling  2 Sample TTest  Survival Times  Count Data
Question: How many conversions are needed for a sequential A/B test?
%  
The Minimum Detectable Effect is the smallest effect that will be detected (1β)% of the time. 

Conversion rates in this range will not be distinguishable from the baseline (onesided test). 
Statistical power 1−β:  Percent of the time the minimum effect size will be detected, assuming it exists  
Significance level α:  Percent of the time a difference will be detected, assuming one does NOT exist 
See also: Simple Sequential A/B Testing