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last updated: 11/9/2010

What Is a Call Number?

Each item in the library (i.e. books, journals, DVDs, etc.) has a unique call number.  The call number is taped to the front or side of an item and is also shown in IUCAT, the online library catalog.    

There are three different types of call numbers:

  • Dewey Decimal: Used by most school and public libraries, these call numbers begin with Arabic numerals.

    Example: 815 GRE

  • SuDocs (Superintendent of Documents): Used by libraries serving as federal depositories (including IU), these call numbers arrange materials by federal agency.

    Example: A 13.3:IR 11

  • Library of Congress: Used by most academic and research libraries (including IU), these call numbers begin with letters of the English alphabet.

    Example: PN6112. G675 2002

What do call numbers mean?

Library of Congress call numbers have several parts that represent different things.  

SuDocs call numbers also have several parts that represent different things.



 Federal Agency or Department (Agriculture)


 Subordinate offices & series (Forest Service, bulletins)
 IR 11


 Item’s subject (Irrigation)

Why are call numbers important?

Library of Congress call numbers are important for two reasons:

1.   The call number is like an address, telling you where an item is located.  Use the Research Collections Map
      to determine which floor you need to go to; then use the tips below to read your call number. 

SuDocs call numbers are important because they differ from LC call numbers in the following ways:

  • It is not a decimal based system.

    Decimal Order

     SuDocs Order

     D 1.1:  D 1.1:
     D 1.12:  D 1.3:
     D 1.122:  D 1.12:
     D 1.3:  D 1.33:
     D 1.33:  D 1.122:

  • The order after the colon follows the, "years, letters, numbers" rule.
    • Years come first
    • Letters come after years
    • Numbers come after years and letters

     Correct Call Number Order

    Example 1

     Example 2

     A 1.35:1993  EP 1.23:1998
     A 1.35:R 42  EP 1.23:A 62
     A 1.35:R 42/1995  EP 1.23:91-44
     A 1.35:R 42/2  EP 1.23:600/1998-103
     A 1.35:321  EP 1.23:600/R-98-23

  • When slashes / and dashes - are involved, remember that nothing comes before something.

     Correct Call Number Order

    Example 1

     Example 2

     C 3.186:  EP 1.23:
     C 3.186/2:  EP 1.23/A:
     C 3.186/7:  EP 1.23/A-2:
     C 3.186/7-3:  EP 1.23/2:
     C 3.186/9:  EP 1.23/2-2:

To learn more about SuDocs or to test your skills please visit Michigan State University's online guide to Learning SuDocs Call Numbers.

2.    Books are arranged by subject, so you can find several helpful books on the same shelf or nearby.  Knowing 
       the letter(s) for your subject area gives you a place to start browsing the shelves.  View the Library of Congress
       Classification Table to find the letters that correspond to your subject.

Ask a Librarian

Need additional help? For further assistance with any topic you can always Ask a Librarian.

SuDocs call number tables borrowed from Fox, B. (1999). SuDocs Basics. Retrieved from,, on June 30, 2007.

last updated: 11/9/2010