Statistical studies of the surface distribution of milled workpieces and the possibility of their use for operation-based tests and machine tool evaluation are presented. In the first part of the paper, the assumptions and scope of statistical research were defined and the method of obtaining data on machined surfaces directly from machining programs was described. In the following part of the article, the results of research consisting in determining the probability of machining operations in the working space of a numerically controlled milling machine are presented on the example of machining programs designed for implementation on the DMC 1035V Ecoline vertical machining center. Knowledge of the load distribution in the working space of a milling machine associated with the machining process can be used to design and manufacture test pieces reflecting the machining tasks performed on the milling machine and to develop appropriate acceptance and evaluation procedures.