Power Usage Effectiveness (PUE) is the most widely recognized efficiency metric in the data center industry and is strongly emphasized within EPI's environmental sustainability and energy management teachings. PUE is designed to show how efficiently a data center uses energy, focusing specifically on how much of the total facility energy actually reaches the IT equipment. The correct formula is:

PUE = Total Facility Power ÷ Total IT Equipment Power

“Total Facility Power” includes all supporting infrastructure: cooling systems, UPS losses, power distribution losses, lighting, security, fire systems, and all auxiliary loads required to operate the data center. “Total IT Equipment Power” refers only to the active IT load such as servers, storage, and network devices.

A PUE value close to1.0indicates optimum energy efficiency, meaning nearly all facility energy is being consumed directly by IT operations. Higher PUE values indicate less efficient facilities where substantial energy is being consumed by overhead systems. This metric is essential for sustainability strategies, capacity planning, and continuous improvement. It allows benchmarking across facilities and helps operators set improvement targets by analyzing where energy losses occur. Because of its simplicity and clarity, PUE remains an industry-standard metric recognized globally.