This Demonstration shows monomer and micellar concentrations in surfactant solutions. In particular, it shows the effect of the relative transition width on the concentration of monomeric surfactant (blue) and micellized surfactant (red) near the critical micelle concentration (cmc). The horizontal axis represents the relative total surfactant concentration. The vertical dashed line at indicates the cmc. The dashed brown curve is a Gaussian function centered at the cmc with half width .