Updated project metadata. Chromatin proteins mediate replication, regulate expression and ensure integrity of the genome. So far, a comprehensive inventory of interphase chromatin has not been determined. This is largely due to its heterogeneous and dynamic composition, which makes conclusive biochemical purification difficult, if not impossible. As a fuzzy organelle it defies classical organellar proteomics and cannot be described by a single and ultimate list of protein components. Instead we propose a new approach that provides a quantitative assessment of a protein’s probability to function in chromatin. We integrate chromatin composition over a range of different biochemical and biological conditions. This resulted in interphase chromatin probabilities for 7635 human proteins, including 1840 previously uncharacterized proteins. Quantitative protein ontologies may provide a general alternative to list-based investigations of organelles and complement Gene Ontology.