CUE (Carbon Usage Effectiveness)

CUE (Carbon Usage Effectiveness) is a sustainability metric that measures the CO2 emissions produced per unit of IT energy consumed in a data center, expressed in kgCO2e/kWh. It is effectively PUE multiplied by the carbon emission factor of the facility's power source, so a facility with a low PUE but a carbon-intensive grid mix can still register a high CUE, and vice versa. The metric was formally standardized in ISO/IEC 30134-8:2022, part of the same data center KPI family as PUE and WUE. An ideal CUE score is 0.0, meaning zero carbon intensity, achievable only with a fully carbon-free power supply such as on-site renewables or a matched power purchase agreement. Unlike PUE, CUE ties facility performance directly to grid decarbonization and renewable procurement strategy rather than pure electrical and mechanical efficiency, and is increasingly cited in operator ESG and net-zero disclosures.