The classification of modern river channels is based primarily on their sinuosity values, which can be determined directly from aerial photographs. Ancient channel systems are seldom sufficiently exposed to allow direct measurement of thalweg and valley lengths, but paleocurrent directions can be used to calculate fairly accurate sinuosity values. Aerial photographs of four modern meander-belts were studied to determine the relationship between local current directions within the meander-belts and the actual sinuosity of the active river channels. A value of 3.2 times the standard deviation gave the best approximation of the operational channel range, resulting in a close correspondence between calculated and actual sinuosity values. This method can therefore be used to estimate the sinuosity of ancient fluvial systems.