We live in societies in which an ever-growing array of activities in a range of fields are assessed, controlled and governed according to quantitative techniques. This paper focuses on processes grounded on quantitative tools (e.g. scores, indicators, rankings, algorithms) that are used in order to measure the performance of processes, people or organizations. Such processes are referred to in this paper as ‘legal metrics’. We explore how different legal systems and sectors rely on legal metrics, and develop a twofold argument. On the one hand, we argue that performance-based quantification often qualifies as a form of regulatory intervention. On the other hand, we contend that performance-based measures are always adopted and applied in legal contexts that react differently to the quantification turn. Both sides of this picture have largely been overlooked by comparative lawyers, even though they imply looking for law in extraordinary places and appraising a variety of legal manifestations in different settings. Understanding which forms of quantitative measures are widespread, in which sectors and regions, made by whom and producing what regulatory effects, is a research task that could (and in our opinion should) be of interest for all comparative law scholars.