In Green IT, Power Usage Effectiveness (PUE) is a calculation used to determine energy efficiency measurements. PUE is calculated by measuring the ratio of total energy consumption-the combination of servers plus the cooling to “useful” energy consumption (just servers). PUE is a green computing tool being promoted by The Green Grid as a way to measure the power delivered to IT equipment in its ratio with its total power consumption in the data center.
The Green Grid measures the following: PUE = Total Facility Power / IT Equipment Power (where Total Facility Power is the power measured at the utility meter. The IT Equipment Power is the actual load associated with all of the IT equipment including computing, storage and networking equipment).