Both temporal and spatial information on rainfall distributions are important in various types of hydrologic studies concerning the determination of runoff characteristics. In reality, rainfall is measured at a point. Hence, for practical purposes, it is necessary to establish some relationships for the transformation of point rainfall at a fixed location to average rainfall over a catchment area in order to provide a more reliable input for rainfall-runoff models. The least equivocal method for deriving values of areal correction factor seems to be directly from frequency curves of areal and point rainfalls. Knowledge of the probability distribution of mean areal rainfall, therefore, is of paramount importance in solving this complex practical problem in hydrology.