The factors affecting flow and mixing of two different fluids in a rotating radial microchannel are investigated using numerical simulation, experiments, analytical approach and dimensional analysis. As has been verified by both numerical simulation and experiments, depending on the channel width-to-height aspect ratio there are two distinctly different modes of operation, subcritical and supercritical modes, that yield identical mixing quality with the supercritical mode providing higher volumetric throughput. Four dimensionless groups (namely, rotational Reynolds number, channel length-to-height, channel width-to-height, and channel initial radial-location-to-height) are found to be important for correlating the quality of mixing of fluids in the rotating microchannel operating in either mode in form of scale-up laws. The latter, which fill the badly needed missing knowledge gap, are useful for design, operation, and optimization of rotating microchannels for fluid mixing. (C) 2014 Elsevier Ltd. All rights reserved.