Large quantities of CO and CO₂ are emitted during conventional steel production. As satellite-based estimates of CO₂ emissions at the facility level are challenging, co-emitted CO can indicate the carbon footprint of steel plants. We estimate CO emissions for German steelworks and use CO₂ emissions from emissions trading data to derive a sector-specific CO/CO₂ emission ratio for the steel industry; it is a prerequisite to use CO as a proxy for CO₂ emissions from similar steel production sites.