Software system families are characterized through a structured reuse of components and a high degree of automation based on a common infrastructure. It is possible to increase the efficiency of software system families by an explicit consideration of process flows in application domains which are driven by processes. Based on that fact this article briefly describes the approach of process family engineering. Afterwards the metrics of Process-Family-Points are explained in detail. These are the only framework to measure the size and estimate the effort of process families. Subsequently this paper shows the first results from a validation of the Process-Family-Points in the application domains of eBusiness and Automotive. After an evaluation of these empirical data this paper concludes with an outlook on future activities.