Power management has become one of the main challenges for data center infrastructures. Currently, the cost of powering a server is approaching the cost of the server hardware itself, and, in a near future, the former will continue to increase, while the latter will go down. In this context, virtualization is used to decrease the number of servers, and increase the efficiency of the remaining ones. If virtualization can be used to positively impact on the data center energy consumption, this new abstraction layer disconnects user services (hosted on a virtual machine) from their operating cost. In this paper, we propose an approach and a model to estimate the total power consumption of a virtual machine, by taking into account its static (e.g. memory) and dynamic (e.g. CPU) consumption of resources. This model permits to reconnect each VM to its corresponding operating cost, and provides more information to virtual infrastructure providers and users to optimize their infrastructure/applications. It can be observed from results of experiments that the proposed method outperforms the methods found in the literature that only consider the dynamic consumption of resources.