An experimental investigation on a solar still with lauric acid as phase change material (PCM) is carried out to examine the effect of both the mass of PCM and basin water on the daily distillate productivity and efficiency of the system under outdoor condition. Basic energy balance equations are written to predict the water and glass temperatures, daily distillate productivity and instantaneous efficiency of the single slope solar distillation system with PCM. It is found that the higher mass of PCM with lower mass of water in solar still basin significantly increases the daily productivity and the efficiency. Therefore, the distillate productivity at night and on day for solar still with PCM increased by 127% and 30-35% respectively than without PCM one. Shukla et al. approach of the use of inner glass cover temperature for productivity prediction which has also been investigated, and the prediction shows relatively better agreement with the experimental data than outer glass cover temperature.