AbstractA laser diffraction technique for the on‐line measurement of crystal growth rates was developed. The crystal growth experiments were executed in a fluidized bed apparatus with a specially designed measuring chamber. It is typical in crystallization from solutions to deal with non‐spherically shaped particles at high suspension densities (3‐25 Vol.‐%). The results achieved in a first approach with commercially available instruments were not understandable. It was shown that the particle size distributions from experiments at high suspension densities depend on the volume concentration. This effect was examined by experiments with constant particle sizes and different volume concentrations.If the volume concentration is detected and used to correct the results achieved for the particle size distribution, understandable and reproducible results can be obtained.The necessary correlation function for the measurements at high suspension densities is int