What is a good PUE value?

PUE of 1.0 is the theoretical ideal where all power goes to IT load. The global average is around 1.5 to 1.6. Hyperscale facilities reach 1.1 to 1.2, while older enterprise rooms often exceed 2.0. The EU Code of Conduct targets 1.5 or better for new build.

How is PUE calculated?

PUE is total facility power divided by IT equipment power. A facility drawing 1500 kW at the meter to power 1000 kW of IT load has a PUE of 1.5, meaning 500 kW is spent on cooling, UPS losses, lighting, and other overhead.

What is DCiE and how does it relate to PUE?

DCiE (Data Centre infrastructure Efficiency) is the reciprocal of PUE expressed as a percentage: 1 divided by PUE, times 100. A PUE of 1.5 equals a DCiE of about 67 percent, meaning two thirds of input power reaches the IT equipment.

Where do I find my grid carbon intensity?

National grid operators and services such as Electricity Maps publish real-time and average carbon intensity in grams CO2e per kWh. The EU average is roughly 250 g, the UK around 180 g, while coal-heavy grids exceed 600 g and nuclear or hydro grids fall below 50 g.

Does a low PUE alone make a data centre green?

No. PUE only measures overhead efficiency, not the carbon of the electricity itself. A PUE of 1.1 on a coal grid can emit more CO2 than a PUE of 1.6 on renewables. Pair PUE with carbon intensity and consider CUE (Carbon Usage Effectiveness) for a full picture.

Data Centre PUE & Carbon Calculator

Power Usage Effectiveness (PUE) is the headline efficiency metric for any data centre or server room. It captures how much of the electricity drawn from the grid actually reaches the computing equipment versus how much is lost to cooling, power conversion, and other overhead. This calculator turns your two power readings into PUE, the inverse DCiE percentage, projected annual energy waste, and the carbon footprint of that waste.

How it works

The core formula is a simple ratio, but the derived figures make it actionable:

PUE   = total facility power (kW) / IT equipment power (kW)
DCiE  = (1 / PUE) × 100%        (efficiency as a percentage)
overhead power = total - IT     (kW spent on non-IT)
annual facility kWh = total kW × 8760 hours
annual overhead kWh = overhead kW × 8760
annual CO2e (kg)    = annual facility kWh × carbon g/kWh / 1000

PUE can never be below 1.0, because the IT load is always part of the total. The gap above 1.0 is pure overhead. Multiplying power by 8760 (hours in a year) gives annual energy, and applying grid carbon intensity converts that to CO2e.

Benchmarks and tips

The ASHRAE and Uptime Institute bands are a useful yardstick: under 1.2 is excellent (hyperscale class), 1.2 to 1.5 is good and meets the EU Code of Conduct target, 1.5 to 2.0 is typical for enterprise rooms, and above 2.0 signals significant cooling or conversion inefficiency. Remember that PUE measures overhead only — a facility on a clean grid with a mediocre PUE can still emit far less carbon than an ultra-efficient one running on coal power. Track carbon intensity alongside PUE to see your true footprint.