Library of Congress Classification System: How to Find Books by LC Call Number

First, convert the call number from the catalog display into a vertical format (as it appears on the spine or lower front cover of the book):
Example: QC 981.8 .G56 D378 2009   becomes: 

First Line: Letters are filed alphabetically.  Single letters are filed before double letters in terms of shelf arrangement.  This series is in 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   KF = Law in the United States  KFC = 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 point subdivisions.

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

Examples:  8701 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 (as above).   The number is read as a decimal (different from the whole numbers used above).

You can see from the example above that .C444 comes before .C64 because when reading the number decimally, each digit is read individually.  4 before 6  (444 as a whole number would come after 64, but as a decimal each digit is read one at a time.

Fourth Line: Publication date.  Filed chronologically.   1999, 2001, 2005, 2011

Fifth Line: Sometimes includes volume numbers (v.2)

The example below breaks the number down line by line:

QA      General subject area is mathematics
76.73      computers (the .73 is specifically for programming languages)
.C 153          for the C++ programming language
S29             Last name of author Savitch
2009              Year of publication