A method is presented by which the time-dependent average termination rate coefficient in an emulsion polymerization may be calculated as an appropriate average of the chain-length-dependent termination rate coefficients. The method takes advantage of the fact that the overall termination rate is dominated by terminations between rapidly moving short radicals and much slower long ones. This termination rate coefficient is suitable for use in the Smith-Ewart equations describing the compartmentalization of radicals in an emulsion polymerization. Rate data in emulsion polymerizations can be quantitatively interpreted if the kinetics fall into one of two categories: zero-one (showing compartmentalization; intraparticle termination is not rate-determining) or pseudo-bulk (no compartmentalization; intraparticle termination is rate-determining). The new method can be used to interpret rate data for systems falling between these categories and also can be used to find termination rate coefficients from Monte Carlo simulations of termination kinetics. The latter is especially useful for predicting and understanding kinetics in controlled radical polymerizations in disperse media.