The knowledge of the time-dependent crystal sizes in batch crystallization processes is a crucial factor. With the basic idea of real-time analysis of crystallization kinetics, in this paper the possible application of the in-situ laser backscattering instruments Focused Beam Reflectance Measurement (FBRM) and 3-Fold Dynamical Reflectance Measurement with Selective Multi Depth Focus (3D ORM SMF) in batch crystallizations is investigated using the example of an inert, particulate model material system. The different, device-specific representation of the particulate model material system is demonstrated.