Purpose - The purpose of this article is to provide a quantitative analysis of the extent to which folksonomies replicate the Library of Congress Subject Headings (LCSH) to see if folksonomies would successfully complement cataloger-supplied subject headings in library catalogs. Design/methodology/approach - The paper compares social tags and LC subject headings for ten books from various library-related applications including next generation OPACs and LibraryThing by ranking tags and subject headings using scales modified from research by Golder and Huberman, Voorbij, and Kipp. Findings - Social tagging does indeed augment LCSH by providing additional access to resources. Research limitations/implications - Several of our applications lacked tags for the books we chose in our study. Tags are primarily taken from LibraryThing. Practical implications - A hybrid catalog combining both LCSH and a folksonomy would result in richer metadata and be stronger than the sum of its parts, giving patrons the best of both worlds in terms of access to materials. Originality/value - This paper supplies quantitative support for the use of folksonomies in a library's catalog. The data also supports many of the previous theories proposed in literature about folksonomies and social tagging. © Emerald Group Publishing Limited.