In the present work, effects of height, length, and width of a single-slope basin-type solar still on its distillate production was investigated. For this purpose, a radiation model was developed which accounts for the influences of all walls on quantities of received solar radiation by the base and saline water of the still. Moreover, in this radiation model, the side walls of the still were considered as the trapezoid and the diffuse as well as beam components of solar irradiance were separately taken into account for the first time. Abilities of the present model were compared with earlier ones. Furthermore, the predictions of the current model were compared with the present experimental results, and it was observed that the predicted and measured values are in a close agreement. The results of this study show that by increasing the height of still's walls, its efficiency decreases. The model suggests that the height of the front wall should be less than about 0.10 m. Moreover, it is illustrated that by extending the still length, the side walls shadow reduces and consequently, the system efficiency increases. In addition, the optimal width to length ratio was found to be about 0.4.