The interfacial tension (IFT) between potassium dihydrogen phosphate (KDP) and solutions of water with a polyol admixture is determined with two experimental techniques. First induction time experiments have been carried out to evaluate the IFT based on the thermodynamic theory of nucleation. Published IFT data is carefully reviewed and compared to the experimental results obtained in this work. Special attention is paid to reproducibility of induction time measurements and to the impact of agitation. The second experimental technique directly determines the IFT on the KDP prismatic face via drop shape analysis (DSA). Provided that the solution does not spread on the crystal surface, drop shape analysis gave reasonable IFT approximations for elevated fractions of the polyol, offering the potential of being a quick alternative method to the time-consuming induction time measurements that typically are of poor reproducibility. However, the most critical aspect about DSA has shown to be the determination of the crystals' surface energy (SFE). Furthermore, for systems with low-IFT values the curvature dependence must be considered, which can be taken into account with the simple Tolman equation.