At the beginning of every empirical study in veterinary medicine is the study planning. This serves to statistically secure the results obtained at the lowest possible investigation costs. At the same time, study planning through the early determination of the required number of subjects is also an active form of animal welfare. After a brief introduction to the statistical and epidemiological foundations, the authors demonstrate the application areas and implementation of various methods for determining sample size using a real example. Case-related exercises allow for self-assessment and direct applicability of the procedures to one's own research topic.