The method reported in this paper is a simple means by which to determine the Avrami exponent, n, after cooling from the molten state of semi-crystalline polymers. This determination, often drudgery, has been significantly simplified, yet remains satisfactorily reliable. It is based on the measurement, from an experimental crystallization exotherm, of the peak maximum and its inflexion points for different cooling rates. Results were tested against the Ozawa theory, and it was found that our method was suitable for a slightly filled or unfilled thermoplastic polymer. However, neither our method nor the Ozawa theory apply when the matrix is reinforced with an efficient nucleating agent.