EVS-EN 50600-4-2:2016

This European Standard specifies the Power Usage Effectiveness (PUE) as a Key Performance Indicator (KPI) to quantify the efficient use of energy in the form of electricity.
NOTE  See the Note 1 to entry in Definition 3.1.3.
This European Standard:
a)  defines the Power Usage Effectiveness (PUE) of a data centre;
b)  introduces PUE measurement categories;
c)  describes the relationship of this KPI to a data centre’s infrastructure, information technology equipment and information technology operations;
d)  defines the measurement, the calculation and the reporting of the parameter;
e)  provides information on the correct interpretation of the PUE.
PUE derivatives are described in Annex C.