Executive Summary

• Power Usage Effectiveness has been an instrumental metric to measure the energy efficiency of data centres, but with the sustainability spotlight intensifying on the industry and more legislation and mandatory reporting, it’s not enough in 2026.
• The metrics that matter more and more in 2026 are The Sustainability Triangle: combining all three metrics (CUE, WUE and PUE).
• Combining accurate, regulatory reports on efficiency and usage with new legislation and policies, the industry is shifting rapidly to ensure it is becoming as sustainable as possible ahead of the 2030 and 2050 pledges.

Power Usage Effectiveness, PUE for short, is an energy efficiency metric for data centres; it’s been around a while, it’s not perfect, but in this sustainability landscape where the industry needs to be net-zero soon, it’s not enough anymore.

It measures the total facility energy divided by IT equipment energy; if the number is closer to 1, it means more efficient energy use – a good thing, of course. But the industry hasn’t solely come into the spotlight over just energy efficiency, so how are we measuring those?

Cue the entry of CUE and WUE (see what I did there?)

CUE, known as Carbon Usage Effectiveness, measures the amount of carbon produced by data centres and is calculated by the total CO2 emissions divided by IT equipment energy. The ultimate aim is to hit 0, which is 100% renewable energy usage and no carbon footprint. This is the ultimate goal by 2050, with separate targets set for data centres by 2030.

WUE, Water Usage Effectiveness, does what it says on the tin, measuring the efficiency of water usage and calculating it by dividing annual water usage by IT equipment energy (kWh). This accounts for water used in cooling systems, humidification and any on-site water usage. Holistic WUE includes water embedded in electricity production, which tends to be higher than the onsite usage.

The Sustainability Triangle

Together, these three metrics form what has been dubbed “The Sustainability Triangle,” which brings together reporting on the three vital elements for a comprehensive and transparent overview of usage and sustainability practices. Power usage effectiveness alone cannot provide a full insight into how sustainable a data centre is; it could also increase carbon emissions or water usage if they aren’t properly tracked, which sets data centres several steps behind in the mission to become 100% carbon free and more efficient with resources.

Data centres need to measure all three to have a balanced efficiency across all domains; these will be the metrics to watch out for this year.

PUE, CUE and WUE reporting

As regulations tighten, efficiency reporting will follow suit to bolster our chances of hitting our ambitious sustainability targets. While the metrics continue to improve, as I’ve said, PUE is not perfect, and many factors can impact the score of a data centre. We need transparent, regulated reporting in the industry so we can see where data centre efficiency needs to be improved before the innovations occur and the industry shifts.

However, we do need regulatory metrics and policies to shift also, and to recognise that data centre infrastructure is becoming complex and nuanced, especially with more high-density, AI workloads taking centre stage as the reasons for the insatiable power demand from data centres.