Basic Cataloging: Intro to Call Numbers

The growth of the online public access catalog (OPAC) and sharing among institutions has added variety to the kinds of library call numbers you may encounter. This FAQ will help you identify what classification system you are dealing with and how to decode the string of alphanumeric characters that make up its call number.

–        Dewey Decimal Classification System (DDC)
–        Library of Congress Classification System (LCC)
–        Library of Congress Control Number (LCCN)
–        OCLC Number (WorldCat)
–        International Standard Book Number (ISBN)
–        International Standard Serial Number (ISSN)
–        Additional Resources

Dewey Decimal Classification (DDC)

The Dewey Decimal Classification system (DDC) is the world’s most widely used library classification system. It was created by Melvil Dewey in 1876 with aims to “organize all knowledge.” It is currently used by public libraries and smaller academic libraries throughout the world as a method for organizing books that ensures books on the same subject are near each other on the shelves. DDC assigns each book a number based on its subject matter. Subjects fall into 10 main classes, 100 divisions and 1000 sections creating a three-digit number that can be expanded with an unlimited number of decimal places to capture additional details about the item. Example: 813.54 M37 2007

Decoding Dewey Decimal Call Numbers

Main Class





American literature in English



American fiction in English



…further narrowing of topic


813.54 M37

Cutter Number identifying author’s name


813.54 M37 2007

Edition date

Patrons of ipl often ask us for help when they want to organize their libraries using Dewey Classification numbers, or need to find Dewey numbers for books they want to add to an existing collection. Unfortunately, the DDC is a proprietary system, currently published by the Online Computer Library Center, Inc. (OCLC) which does not make a complete listing of DDC available online for free.

Small libraries may find that the level of detail provided by the free online resources is sufficient to meet their needs. Larger libraries will probably find that they need to buy a new or used copy of the multi-volume DDC or subscribe to WebDewey, OCLC’s commercial product, in order to organize their collections effectively. TheDewey Decimal Classification Home Page provides information about the products available for purchase or subscription.

Dewey Decimal Classification summaries:  down to the third level (section) for free:

The University of Illinois at Urbana-Champaign (UIUC) Library also provides the Summaries of the DDC down to the third level (section), along with explanation in the “Anatomy of a Call Number”:

Introduction to the Dewey Decimal Classification, a downloadable pdf file, explains the DDC system in greater detail.

You may also want to try out the Dewey Browser Beta (OCLC), which allows you to search or browse millions of records from OCLC’s WorldCat database. DDC summaries down to the third level are provided as browsing links and for each result. Click the DDC number in a result to see them.

Another great resource is Classify: an experimental classification web service (OCLC): Enter a title, author, OCLC number, UPC, or ISSN and it will retrieve summary information from Web Dewey (DDC commercial site) and Classify Web (LCC commercial site) displaying the most frequent call numbers for the item in both DDC and LCC format.

Library of Congress Classification (LCC)

The Library of Congress Classification (LCC) is the system of classification used in most research and university libraries in the United States. LCC was created in 1891 specifically to meet the needs of the Library of Congress collection. It is based on twenty-one classes designated by a single letter. These are divided into subclasses that add one or two letters to the initial class. Topics within the subclasses are assigned whole numbers which can be expanded into decimals to identify more specific areas of the topic. This is followed by an alphanumeric author identifier which may be followed by publishing date and other details to produce a unique call number for the item. As with DDC, depending on the level of specificity needed, the call numbers can get fairly long.  Example: PR9199.3.M3855 L54 2007 c.2

Decoding Library of Congress Call Numbers



Lanuage and Literature



English Literature

Topic Area


…English literature: Provincial, local, etc.      



…further narrowing of topic



Cutter Number identifying author’s name


PR9199.3.M3855 L54

Cutter Number identifying title


PR9199.3.M3855 L54 2007

Edition date


PR9199.3.M3855 L54 2007 c.2

Additional details about the item

Effective July 1, 2013, the Library of Congress discontinued print publication of its classification system. (Press release announcing the change.) Due to reduced demand, LC decided to transition to web-only publication of its cataloging documentation. Going forward, LCC subject headings, classification schedules and other cataloging publications will be released as downloadable pdf files free of charge from the Acquisitions and Bibliographic Access Directorate website.

The Library of Congress will continue to offer two web-based subscription products that provide a higher level of functionality for institutions requiring more assistance cataloging their collections. Details and pricing for the paid versions, Cataloger’s Desktop and Classification Web, are available through LC’s Cataloging Distribution Service.

Library of Congress Classification PDF Files: List of currently available, free classification schedules which should be updated as the conversion from print to web continues.

Library of Congress Classification Outline: Free online list of main classes with links to view or download subclass outlines that include topic areas.

Library of Congress Catalog: Search for titles in your collection to locate call number.

Fundamentals of Library of Congress Classification. Complete course materials from the LC’s “Cataloging Skills” workshop to view or download as pdf file. Excellent resource.

Video – Library of Congress Classification System: Instructional video explaining how to read LC call numbers and use them to locate materials in the library. This is part of the Storms Research Center YouTube Channel offering library-related resources.

As mentioned in the DDC section, a helpful cataloging resource is Classify: Enter a title, author, OCLC number, UPC, or ISSN and it retrieves summary information from Web Dewey and Classify Web displaying the most frequent call numbers for the item in both DDC and LCC format.

Library of Congress Control Number (LCCN)

The Library of Congress Classification system (LCC) should not be confused with theLibrary of Congress Control Number (LCCN) system. The LCCN is a unique identification number assigned by the Library of Congress to the catalog record of each book, and some authors, in its cataloged collections. The number has nothing to do with the contents of the book, its sole purpose is to identify the individual record to facilitate sharing of records with other libraries. LCCN has been operating since 1898, originally as the Library of Congress Card Number since the bibliographic data was stored on physical cards. Today’s LCCN includes a LCCN Permalink, a persistent URL addresses for each record to facilitate centralized cataloging in the online environment. Example: LCCN 2010549727 and LCCN Permalink http://lccn.loc.gov/2007281064

OCLC Number (WorldCat)

WorldCat is the world’s largest online public access catalog (OPAC). It holds millions of records from public and private libraries around the world, serving as a powerful resource for locating and cataloging material. All catalog records from member libraries that are submitted to OCLC are given a unique accession number. These individual records are compared with other holdings to eliminate duplication. If the item is original, it becomes the master record. If not, it is associated with the master record number for that item. This number, the master record number, is displayed in the record listing, not the DDC or LCCN numbers that accompanied the original local bibliographic records. OCLC and WorldCat are beyond the scope of this guide, but knowing where to find the OCLC number in a WorldCat record can help you retrieve the most common DDC and LCC call numbers usingClassify. Example: OCLC 154690024

International Standard Book Number (ISBN)

The ISBN is a 13-digit, or 10-digit (pre-2007), number used to uniquely identify books and similar material published internationally since 1970. Most books published after 1975 have been assigned an ISBN; those published after 1985 will likely have a barcode with the ISBN on the back cover. The ISBN is composed of: location identifier, publisher identifier, title identifier, and ending with a single-digit checksum; the 13-digit ISBN added a 3-digit prefix. The number does not convey any information about the book’s subject or author that could help with shelving or locating related material. The ISBN can, however, be used to locate collection items in WorldCat, Amazon, and other online sources of bibliographic data. Examples: ISBN 0-151-01383-7 and ISBN 978-0-151-01383-8

International Standard Serial Number (ISSN)

The ISSN is an 8-digit number divided by a hyphen used to uniquely identify periodical publications internationally. There are actually two types: p-ISSN is for print periodicals and e-ISSN/eISSN for electronic periodicals. The ISSN identifies a specific magazine title only, not an individual issue, publisher or location. For this reason, a specific issue of a periodical may have both an ISSN and ISBN.  Example: ISSN 0009-7675

Additional Resources

ipl cataloging resources: directory of additional web resources on cataloging and classification systems.

Comparison of Dewey and LOC classification numbers:

DDC to LCC classification conversion tool offered by QuestionPoint (OCLC):

LCC to DDC classification conversion tool offered by QuestionPoint (OCLC):

WorldCat’s Expert Search: WorldCat allows users to specify which field(s) to search, including Dewey and LC call number fields, by adding a prefix index label to the search query. Example: dd:813.54M or lc:PR9199 where dd: signifies a search for the Dewey call number 813.54M, and lc: searches for the LC call number PR9199. Other prefixes include: bn: for ISBN, sn: for ISSN, and nl: for an LC Control Number. The is a useful way to check your cataloging. Details on the index labels available:

Library of Congress Cutter Table: The Cutter table is used to create a unique alphanumeric code identifying the author for use in differentiating similar items in a collection. It is typically a single letter followed by a 2- to 4-digit number, depending on which Cutter Table is used and the specificity required. Some LCC call numbers include a cutter for the author and one or more to further specify the subject. These are used in both DDC and LCC call numbers.

OCLC offers a downloadable application that creates Four-Figure Cutter numbers for you (Windows only)

Updated by Jill Wiercioch Spring and Summer 2013.