Numerous studies on power consumption in mixing vessels have been reported, and several power correlations have been developed for non-baffled mixing vessels, for example, Nagata's correlations. However, baffled mixing vessels with different impeller geometries have different power numbers. In this paper, the effects of vessel bottom shape, number of blades, and impeller position on power number were measured for several impellers with geometries that had been assumed to have the same power in Nagata's concept. It was found that power numbers in baffled vessels varied greatly with impeller geometry, while Nagata's concept is valid for non-baffled vessels, regardless of impeller position.