A method for calculating the average aggregate mass of individual molecules in a sample, where the molecules in solution associate to form clusters. Data sets of average aggregate mass of the sample versus concentration of the sample in the solvent are generated. The basic principles and technology in generation of the data is the well understood action of a solute upon the solvent vapor pressure above the solution. By observing the effect of a sample solute on the temperature/vapor pressure properties of a solvent, if is possible by known methods to determine its average aggregate mass. When dealing with a solute material that tends to form clusters, however, the average aggregate mass found is an apparent average aggregate mass, i.e. the average aggregate mass of all of the particles, which are the clusters and any unassociated molecules, if any. To determine the true average aggregate mass, a method employing the determined apparent average aggregate masses, referred to herein as the BRD method, is used. Since the method is based upon cluster thermodynamics and equilibrium properties, it reflects more accurately the behavior of the clusters at various dilutions. The method provides a basis for the prediction of thermodynamic and equilibrium properties, which was not possible with previous methods.