In today’s technology driven world, use of cloud technology is ever increasing. To sustain the increasing demand, new data centers are coming up quite fast. Also, the equipment in these data centers is scaling up. Energy consumption by these data centers has opened a new front of research. Not only the energy consumption has to be minimized, but the carbon footprint needs to be arrested to minimize the environmental hazards. Energy usage and dissipation takes place in different forms. Customized metrics are required to evaluate the performance of these centers. We have classified the major efficiency metrics according to their importance in a given scenario. Different scenarios have been identified for the suitability of these metrics along with the formulae to calculate these metrics. Two new metrics namely Energy Eat by Servers and Switches (EESS) and Energy Eat and SLA violation Factor (EESF) have been proposed.