Web service enabled Service Oriented Architecture has been an increasingly popular approach for enterprises to develop an agile and flexible architecture. However, very little guidance on the granularity of “services” has been provided, which has an impact on the trade-off between flexibility and coordination effort. We suggest that the lack of granularity guidance is due to the lack of the explicit positioning of “services” in the traditional enterprise architecture literature. After clarifying the relationship between “services” and “processes”, we provide an approach to define “process complexity” along certain dimensions and use this complexity metric to decide on the appropriate granularity of the “services”.