In the course of business process management, processes can be represented by models in order to document, analyze and improve processes. Many analyses of business process models require the cal-culation of similarity values between activities of different process models. Process models can be cre-ated using domain-specific business process modeling languages. These languages provide predefined domain-specific sets of activities and their properties and allow the annotation of property values based on glossaries. Since this information describes activities in detail, it enables a precise calculation of similarities between process model activities. However, the literature does not provide a suitable simi-larity calculation for two activities in different process models created with the same domain-specific process modeling language. Consequently, relying on design science research the contribution of this paper is to propose such a similarity metric. The metric incorporates annotated property values of ac-tivities and considers the properties’ different relevance, takes into account the characteristics of quan-titative properties and analyzes the contexts of activities. The metric is conceptualized and demonstrated by an example. Future research requires its technical implementation and evaluation.