A method to determine the agglomerate and aggregate sizes of carbon black (CB), commonly used in anode and cathode suspensions for lithium-ion battery electrodes, is presented. An analysis via light diffraction and scattering was evaluated, and measuring parameters and the development of sample preparation are described in detail. Within this work, different dispersing additives were tested with regard to their ability to stabilize the CB agglomerates and aggregates after dispersing. Furthermore, a sample preparation routine was set up which enables the determination of CB particle sizes in about 10 min. This includes the separation of active material particles and the particle size analysis itself. Furthermore, the method was tested with discontinuously and continuously processed suspensions using a laboratory dissolver and a pilot-scale extruder. In these experiments, the progress of CB deagglomeration in the dispersing step could be proven. For this reason, the method represents a suitable instrument for a quality check in an early production stage.