During this research, the catalogues of more than 200 libraries and museums of Hungary and its neighboring countries were examined. The authors calculated the amount and the size of the metadata and of the full content records in the databases of their collection management systems, as well as the size and the type of the full content data and the size of the databases. By analyzing the results, the goal was to answer the following three questions: (1) Can any significant difference be established between the results according to country, nationality, or type of institution?; (2) How large is a metadata record or a full content record?; (3) Is it possible to establish a methodology for selecting a representative sample of institutions to facilitate further research? For planning the costs of data management, the size of the databases, the number of metadata records, and the variability of metadata and media records shall all be considered. A distinction should be made between the indispensable “primary” data to be preserved for a long time, and the “secondary” data units which are derived from the primary data. It is investigated in this article how to establish the size of primary data in the databases of collection management systems.