PUE

Power Usage Effectiveness (PUE) is a metric used to measure the energy efficiency of a data center. Developed by The Green Grid in 2007, it compares the total amount of energy a data center draws from its power sources with the amount of that energy consumed by IT equipment.

PUE is defined as the ratio of Total Facility Energy to IT Equipment Energy. Total Facility Energy includes all energy used within the facility, such as cooling, lighting, power delivery, uninterruptible power supplies, and auxiliary systems. IT Equipment Energy covers the energy used by servers, storage, and network gear. Measurements are typically taken over a defined period (monthly or yearly) using metered data, with boundary definitions affecting the result.

Interpreting PUE is straightforward: lower values indicate greater overall efficiency, with 1.0 representing the theoretical optimum where all facility energy directly powers IT equipment. In practice, modern data centers often report PUE values between 1.1 and 1.5, while older facilities may exceed 2.0. Improvements come from efficient cooling and airflow management, high-efficiency power and cooling infrastructure, and better IT equipment efficiency, as well as practices like hot or cold aisle containment and virtualization to increase IT utilization.

Limitations of PUE include that it does not measure IT equipment efficiency or utilization directly, and it can be affected by how and when measurements are taken or what loads are included in the facility energy. As a result, PUE is most meaningful when tracked consistently over time and supplemented with other metrics such as DCiE, CUE, or WUE to provide a more comprehensive view of data center performance and sustainability.