We present in this article a comparison of the light scattering cross-section obtained by using exact calculations (GMM code computed by Xu) and several approximated methods such as the Compact Sphere (CS), Anomalous Diffraction (AD), Effective Refractive Index (ERI) and Percival–Berry–Khlebtsov (PBK). We carry this out, for different shapes of aggregate (i.e. compact and linear configuration) consisting of different numbers of primary particles (2, 4, 8, 16, 64, 100). We study it as a function of a size parameter of the primary particles in the range from 0 to 10 and as a function of the type of materials (SiO₂, Al₂O₃, TiO₂). We present the validity range of these approximated methods and conclude that ERI is the most promising one for all the ranges of size parameter (i.e. the average error of this method is, compared to the exact method, around 3% for a compact configuration).