When the number of defectives (nonconforming products) is to be used as the response in two-level factorial and fractional factorial experiments, it is helpful to have an estimate of the sample size necessary for detecting a specific change. In this article we provide an easy-to-use table for standard 8, 16 and 32 run two-level factorial experiments that serves as a guideline for the necessary sample sizes to detect different changes in the average quality level. Examples of the use of the table are also provided.