Sizing of particles in industrial processes is of great technical interest and therefore different physical-based techniques have been developed. The objective of this study was to review the characteristics of modern sizing instruments based on a modified fibre-optical spatial filtering technique (SFT). Fibre-optical spatial filtering velocimetry was modified by fibre-optical spot scanning in order to determine simultaneously the size and the velocity of particles. Sizing in-line instruments of Parsum GmbH use these measuring principles and may be adapted to different process conditions. Particles with sizes of 506000 mu m and velocities up to 50 m/s may be measured by the probe system IPP 70. An overview is given to real-time sizing of particles in different technical applications: fluid-bed granulation, high shear wet granulation, Wurster coating, mixing, spray drying, crystallization and milling. (C) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.