Y junctions with a large width-to-depth ratio were used for the emulsification of hexadecane in various ethanol-water mixtures with different static interfacial tension and viscosity. The resulting droplets were monodisperse. To describe droplet size a force-balance model was derived and was found to apply well. The model shows that the droplet size scales with the channel depth, and with the square root of the inverse capillary number (Ca-1/2) based on the continuous phase, the disperse-phase flow rate was found to be unimportant.