When developing new solvent extraction processes, one often has to evaluate new solvents, new aqueous phases, or both for their ability to work in plant-scale equipment. To facilitate solvent characterization, a simple test is proposed based on the dimensionless dispersion number (N-Di). It allows one to characterize the ability of the solvent to separate from a two-phase dispersion and to estimate process throughput for equipment of a given size. Several ways to carry out the N-Di test are given, including a standard test procedure. The N-Di test was applied to the performance of solvent extraction equipment with discrete process stages, the leaching of plasticizers from plastic tubing, and the development of a new solvent for the combined extraction of strontium acid transuranic elements.