In this paper, we present a brief overview of the current work that has been undertaken for a few years to build the FIRMS Global Tuna Atlas (GTA) which requires compliant conversion factors for the conversion of catch from numbers to weights. We first discuss the current conversion factors provided by tuna Regional Fisheries Management Organisations (e.g., IOTC) and by the French Institute of research for development (IRD). Eventually, we present a plan to validate conversion factors for scientific purposes