To fulfill their missions, humanitarian organizations are engaged in the production and dissemination of a specific form of knowledge about refugees – namely, evidence. Yet relatively little scholarly work has been done on evidence as a basis for humanitarian decision-making in refugee crises. In this article, we analyze the evidence produced on Syrian refugees in Jordan between 2012 and 2017 by humanitarian actors, its appropriateness and relevance, to assess a) potential side-effects for refugees and b) functions for humanitarian organizations. Drawing on 234 documents on Syrian refugees in Jordan collected on major humanitarian platforms and interviews with experts from international organizations, this article shows that, due to the type of evidence produced, Syrian refugees living outside camps are invisibilized and their needs might be less considered in aid projects. The article also shows that some evidence practices are related to the outsourcing of data collection and analysis to specialized actors, and to a quantification and standardization of evidence that plays a part in consolidating the legitimacy of humanitarian organizations. Our results highlight the importance of considering this specific form of knowledge when studying humanitarian interventions in international migration and refugee governance.