Chapter 09 · Sustainability & AIClimate & Environment
Power Usage Effectiveness (PUE)
Definition
Power usage effectiveness is a ratio metric, developed by The Green Grid in 2007, expressing data centre energy efficiency as total facility energy consumption divided by IT equipment energy consumption. A PUE of 1.0 would mean all energy powers computing with none lost to cooling, power conversion and other overhead; modern hyperscale facilities achieve values around 1.1–1.2, while older facilities may exceed 2.0.
References
This source provides part of the technical or institutional basis for the definition.
This reference provides supporting context for how “Power Usage Effectiveness (PUE)” is defined and used.
Overview
Limitations
PUE measures facility energy overhead relative to IT equipment energy. It does not measure total electricity demand, grid carbon intensity, water use, embodied impacts from buildings and hardware, or the useful work produced by computing. A lower PUE is therefore not an overall sustainability score.
How it is used
Operators report PUE for benchmarking and customer commitments; regulators increasingly mandate disclosure (e. g. , the recast EU Energy Efficiency Directive's data centre reporting rules).
Why it matters
As digitalisation and AI drive electricity demand growth, PUE remains the reference metric separating efficient from wasteful facilities — and a reminder that efficiency metrics must be read alongside absolute consumption.