Abstract The densities and pH of partially carbonated aqueous ammonia solutions were measured at 20 °C. With increasing carbon dioxide loading, increases in density and decreases in pH were observed. These results were used to produce correlations for aqueous ammonia solution loading as a function of ammonia concentration, density, and pH. The correlations are based on first principles to increase predictive capabilities. The predictive capacity of three correlations, having different complexity, was compared. The ensemble of models using both density and pH proved to be superior to correlations based on density or pH separately.