In the present work, a unified formulation has been applied to predict the tensile curves of ferrite, pearlite, bainite and martensite. This model produces a Voce type of equation that has been successfully applied to fit the experimental tensile curves obtained with the above mentioned microstructures. This allows testing the model over the broad range of tensile strengths that are associated to the different microstructures produced by the transformation of the austenite. The results are treated in a unified way and discussed in terms of a characteristic size for each microstructure type and the size variations within each range.