A light-scattering instrument that is normally used for particle size analysis was applied to obtain information about particle shape. Micro-cuboids of dimensions a x b x c in the range between 10 and 1000 mu m, which can be accurately manufactured employing special technology, were used as labelled samples for the determination of 3-D features. Particle projections at different orientations due to turbulent motion were measured sequentially. The laser diffraction of cuboids rotating in a turbulent flow is described theoretically using a simplified model, i.e. rotation of a rectangle. The change in the projection areas of rotating cuboids is connected with their rotational velocity. The power spectrum density of rotational velocity of cuboids and spheres was determined and the influence of particle shape on the power spectrum density established. The frequency distribution of projection sizes was found to be suitable for particle shape estimation.