The invention relates to a method for determining the average radius of gyration (rg) of particles with a size of ≤1 μm in a suspension, and to a device for carrying out the method according to the invention. The method is based on the scattering of linearly polarised electromagnetic radiation on nanoparticles, which, suspended in a solution, are moved through a through-flow cell. The irradiation is carried out perpendicular to the movement direction, wherein the scattering intensity is measured via at least four detectors that are arranged in a defined plane at defined angles. Alternatively, at least one mirror can be used in the position of at least one of the detectors, which deflects the radiation to at least one detector. Based on the scattering intensities, both the average radius of gyration (rg) of the particles as well as the concentration thereof in the suspension can be determined.