Business Process Models (BPMs), often created using a modeling language such as UML activity diagrams, EventDriven Process Chains Markup Language (EPML) and Yet Another Workflow Language (YAWL), serve as a base for communication between the stakeholders in the software development process. In order to fulfill this purpose, they should be easy to understand and easy to maintain. For this reason, it is useful to have measures that can provide us adequate information about understandability and maintainability of the BPM. Although there are hundreds of software complexity measures that have been described and published by many researchers over the last few decades, measuring the complexity of business process models is a rather new area of research with only a small number of contributions. In this paper, we provide a comprehensive report on how existing complexity metrics of software were adapted in order to analyze the current business process models’ complexity. We also proposed a GoalQuestion-Metric (GQM) framework for measuring the understandability and maintainability of BPMs.