An extensive lumped model was developed for butyl acrylate emulsion polymerisation. Monomer volume fraction in the particle was calculated using a thermodynamic equation and the average number of radicals per particle was calculated according to a relationship given for the pseudo-bulk kinetics. The model also incorporated both the micellar and the homogeneous nucleation phenomena and incorporated individual oligomer balances for radicals arising from initiator decomposition and further propagation in the aqueous phase. The model also explored the effects on polymerisation kinetics of including radical exited from the particles in the aqueous phase radical balance. The effects of considering entry in the micelles and the particles of only radicals of a certain chain length were also studied. The model was validated against the experimental data taken from the literature.