The aim of this study is to express the impacts of building-related sustainability measures in a generic set of performance indicators, exploiting fine-grained city data. A data enrichment method is described for energy consumption data and municipal administration data, that gives accurate estimations of the current energy performance of buildings in a city. The impacts of 11 building-related sustainability measures are approximated using these enriched data. These impacts are then expressed in the four KPIs (1) CO2 emissions, (2) energy efficiency, (3) share of renewables and (4) costs, which enables comparison between the 11 sustainability measures, while taking into account local conditions. In combination with a decision support tool developed within the EU's transform programme, it enables city stakeholders to focus their efforts more effectively, accelerating the transformation of our cities into low carbon cities.