The effect of surfactant concentration on particle nucleation in emulsion polymerization of n-butyl methacrylate has been studied using sodium dodecyl sulfate as the surfactant and potassium persulfate as the initiator. The rates of reaction as a function of time were determined for surfactant concentrations above and below critical micelle concentration of the surfactant. The order of dependence of the particle number on the surfactant concentration was found to be different in different ranges of surfactant concentration. This has been explained on the basis of the predominant phenomenon that affects particle nucleation in each range of surfactant concentration. In the range where the end of particle nucleation is determined by a critical surfactant coverage necessary for colloidal stability, the particle number is expected to increase in proportion to the third power of the surfactant concentration. It has been shown how a size-dependent volumetric growth-rate of particles can result in different exponents in the Smith-Ewart equation relating the particle number to surfactant concentration. A constant volumetric growth rate of particles is assumed in the Smith-Ewart theory of particle nucleation.