<p>The carbon footprint of electricity is a critical metric for climate policy and corporate sustainability reporting, yet its quantification is hampered by a lack of methodological consensus and a fragmented evidence base. This fragmentation reflects a central debate in industrial ecology regarding the consistency and comparability of life-cycle-based emission factors across different modelling paradigms. This study addresses this gap by performing a systematic, quantitative comparison of electricity emission factors from a wide range of authoritative sources, including process-LCA databases (Ecoinvent), environmentally extended input–output tables (EXIOBASE, EMERGING, EORA, GLORIA, GTAP), primary agency data (IEA), and others. We harmonize technology taxonomies and GHG characterization factors to compare technology-level and national-level emission factors for the EU and the US. Our findings indicate that, for technology-specific emission factors, there is a moderate level of agreement regarding direct operational emissions (direct carbon intensity). However, we observe substantial and systematic variation when it comes to full life-cycle carbon intensity. These discrepancies propagate to national-level estimates, where a country’s calculated carbon intensity can significantly vary, solely based on the data source chosen. This paper provides a useful reference to deconstruct and understand such divergences. We operationalize these findings into a set of practical selection criteria that enable analysts and decision-makers to make transparent and context-appropriate choices. We conclude that a more transparent and critical approach to sourcing emission data is fundamental to the credibility of carbon accounting and the broader energy transition.</p>