A microscopic cross-linking model has been applied to calculate the Young's modulus as a function of heat-treatment temperature (HTT) of petroleum coke (a graphitizable carbon) and Akabira coal (a non-graphitizable carbon). This model is an extension of a previous model for non-graphitizable carbons, where not only the coalescence of crystallites along the c axis, but also the coalescence along thea axis has been accounted for. The model explains the maximum of the modulus of both carbons at about 1200°C HTT, although it does not correctly predict the experimental values above 1500°C for the graphitizable carbon. This discrepancy is attributed to the elasticity of the individual crystallites, which were assumed as rigid bodies in the model.