How to Find the Dewey Decimal Number for a Book

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The Dewey Decimal Classification (DDC) system, invented by Melvil Dewey (1851-1931), is the most popular method of logically categorizing and organizing library books according to subject. (A different system is used by many university libraries.) When you are hunting for a book in a library, its Dewey Decimal Number—along with the help a librarian or wall map—enables you to zero in on its exact location in the library stacks.

    Become acquainted with the basic categories of the Dewey Decimal System. The broadest classes are 000-099 (general reference), 100-199 (psychology and philosophy), 200-299 (religion), 300-399 (social sciences), 400-499 (language), 500-599 (natural science), 600-699 (applied science), 700-799 (fine arts), 800-899 (literature) and 900-999 (history).

    Search the library's database. If you are looking for a specific book, to find it quickly you need at least the title or author. Either allows you to easily retrieve the Dewey Decimal Number from the library’s database, using a computer terminal available to patrons. You may need to scan several entries if the title or the author name is a common one. If the library’s computer system is new to you, a librarian show you how to navigate it.

    Paper card catalogs have mostly gone the way of the dodo bird. But where such drawers are still used, cards are typically organized by author, title and subject.

    Learn more about subcategories within each broad subject range. More detailed knowledge of Dewey Decimal Classification is useful if you know only the subject you are interested in, or wish to browse the shelves for any books currently available on that subject. Several websites provide relatively detailed listings of Dewey Decimal classes, divisions and sections (see Resources).

    The University of Illinois at Urbana-Champaign’s “Guide to Call Numbers” lists a hundred subcategories for each broad category. For example, in the 100s section, we find 171, systems and doctrines; 172, political ethics; 173, ethics of family relationships; 174, economic and professional ethics; 175, ethics of recreation and leisure.

    According to Dewey Services, the DDC system, now in its 22nd edition, runs to four volumes in its exhaustive print version. For many research projects, however, any fairly recent abridged version will suffice.

    Look in the stacks of shelves. Once you have the Dewey Decimal designations you need, visit the sections of the library that house them. Larger libraries provide maps showing on which floor or section the various Dewey categories may be found. In smaller libraries, the books may be arranged in easy-to-follow numerical order on a single floor.

    Things You'll Need

    • Book title and/or author, or book’s subject
    • Outline of Dewey Decimal System
    • School library or public library
    • Library database or card catalog


    • Not only beginners need librarians; very experienced researchers often take pains to credit a librarian for assisting with a project. Consult a librarian for information about how the library might have alternately categorized books with multidisciplinary subject matter, or about other aspects of your research. Nobody knows the library’s own resources better than the professionals who work with them every day.

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