In situ measurement techniques are promising tools to aid process development. However, they also pose new challenges in evaluating large amounts of recorded data. A new procedure for in situ laser-backscattering devices has been developed that allows transformation of the raw recorded data, a chord length distribution, into a format suitable for population balance modeling. Emphasis is thereby laid on the influence of the suspension density on the measured data. Experimental data are recorded using a batch laboratory crystallizer equipped with an in situ 3D-ORM laser backscattering device and an ultrasound probe. The new proposed five-step procedure for data preprocessing is based on several independently developed tools from literature and is exemplarily illustrated with results on the crystallization of ascorbic acid. The proposed method is a step forward to use in situ laser-backscattering devices also for quantitative purposes.