Google announced that its trailing 12-month average PUE (power usage effectiveness) was approximately 1.14 — an improvement from 1.16 in 2010. PUE is a ratio of the total power used to run a data center to the amount used to power the servers.
Google said its calculation includes everything that contributes to energy consumption in its data center — not just power for servers and cooling systems. It also includes heating/cooling for the office, system inefficiencies like transformer, cable and UPS losses and generator parasitic energy draw. Otherwise, the number would have been even lower.
http://www.google.com/about/datacenters/inside/efficiency/power-usage.html
