A simplified model is developed to calculate the modulus of carbon black filled rubber compounds by using standard characterization data of the filler, its volume fraction and only one fitting parameter: the number of junctions between neighboring carbon black aggregates. The model is based on three hypotheses with respect to (1) the optimal dispersion of aggregate, (2) the pure physical nature of rubber-carbon black interactions, and (3) the possibility to describe aggregates essentially in terms of specific surface area and structure, both accessible through standard characterization methods. Average rubber-filler interactions are introduced through microme-chanical considerations. The model is probed by using dynamic strain sweep test results on two series of carbon filled compounds, one on the basis of SBR1500 Emulsion Styrene-Butadiene Rubber, the other on RSS3 Natural Rubber. It is found that the number of junctions is decreasing with increasing strain amplitude, thus, offering a clear explanation for the well known dynamic strain softening effect. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 599-607, 2011