What Is PUE (Power Usage Effectiveness)?
PUE is the standard metric for data center energy efficiency. It is the ratio of total facility power to the power actually delivered to IT equipment.
The formula
PUE = Total facility power ÷ IT equipment power
A PUE of 1.0 is the theoretical ideal — every watt goes to IT. A PUE of 2.0 means the facility uses one watt of overhead (cooling, power distribution, lighting) for every watt of IT load.
What PUE Actually Measures
Power path
UPS, PDUs, transformers, and distribution losses.
Cooling
CRAC/CRAH units, chillers, pumps, and fans — usually the biggest overhead.
Everything else
Lighting, security, and building systems.
PUE Under AI-Era Pressure
As GPU density and rack power climb, cooling overhead grows and PUE comes under scrutiny — from cost, from sustainability reporting, and from regulations like the EU Energy Efficiency Directive. But PUE is a facility average. Improving it requires acting at the device and rack level, where the energy is spent.
Measure your PUE, then make it actionable
Use the calculator to benchmark, then connect device-level power and cabinet thermal data to actually move the number.