Anchor impellers are commonly used for the homogenization of non-Newtonian fluids, often in association with a set of coaxial turbines. The optimal design of such mixers relies on the knowledge of power drawn by the individual impellers. In non-Newtonian mixing, this can be readily obtained using the Metzner-Otto (1957) concept. In this article, the Metzner-Otto concept and the determination of the constant K-s for anchor impellers have been revisited using numerical and experimental techniques for the case of shear-thinning and shear-thickening fluids. Contrary to literature findings, it is shown that the constant K-s does not vary strongly with the power law index and that, for mixer design purposes, the use of a constant value of K-s for each of the rheological behaviors considered is adequate.