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Library of Congress Classification System: How to Find a Book in the Library

What is a Call Number?

A call number is like an address for a house. It tells you where an item is located in a library. Each physical item owned by a library has its own unique call number. 

Call numbers appear two different ways, depending on where you view them:

on the spines of the books and in the online catalog.

Note that the same call number can be written from top-to-bottom or left-to-right. 

In the example below from the OneSearch Library Catalog, notice the placement of the call number in the record. Call numbers are listed after the availability of the item and its owning library.

call number screenshot

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Line-By-Line Description

First Line

Letters are filed alphabetically. Single letters are filed before double letters in terms of shelf arrangement.  For example, this series is in the correct order:  D   DA   DF   DL    DT

The first letter indicates a very broad subject area, which is made more specific by adding a second and sometimes third letter.  

K = Law in general
= Law in the United States
= Law in California

Second Line

This line is read as a whole number. Numbers on the second line can range from 1 to 9999 and can also have decimal points.

Example: 32 (thirty-two) is shelved before 310 (Three hundred ten).  Any number followed by a decimal point is filed decimally.

Examples8701 is shelved after 8700.7          8700.7 is shelved after 8700.17

Third Line

This line begins with a decimal point, followed by a letter and number sequence.  The letters are read alphabetically and the number is read as a decimal.

      Will Appear Before           




Fourth Line

Publication date, shelved in chronological order.   1999, 2001, 2005, 2011

Fifth Line

Sometimes includes volume numbers, possibly the copy number (if multiple copies exist of an item in a library).  Items filed chronologically: (v.1, v.2; c.3, c.4)