Current classification of fluxes is typically on the basis of a qualitative process with parameters like residue activity in a water extract or the ability to dissolve copper in a thin mirror film. The capability of quantitatively ranking fluxes by their total reaction capacity and reaction rate with copper oxide would provide valuable data for process design. Results are reported of experiments to establish a standard procedure to measure a flux activity number using a controlled reaction of a measured amount of flux reacted with an excess of a standard metal oxide.