-Process metrics can be used to establish baselines, to predict the effort required to go from an "as-is" to a "to-be" scenario or to pinpoint problematic ITSM process models. Several metrics proposed in the literature for business process models can be used for ITSM process models as well.This paper formalizes some of those metrics and proposes some new ones, using the Metamodel-Driven Measurement (M2DM) approach that provides precision, objectiveness and automatic collection. According to that approach, metrics were specified with the Object Constraint Language (OCL), upon a lightweight BPMN metamodel that is briefly described. That metamodel was instantiated with a case study consisting of two ITSM processes with two scenarios ("as-is" and "to-be") each. Values collected automatically by executing the OCL metrics definitions, upon the instantiated metamodel, are presented.Using a larger sample with several thousand meta-instances, we analyzed the collinearity of the formalized metrics and were able to identify a smaller set, which will be used to perform further research work on the complexity of ITSM processes.