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How to read Library of Congress Call numbers


Library of Congress call numbers can be confusing since they frequently contain a letter or letters followed by whole numbers, and then a letter followed by decimal numbers. In reading a call number, begin at the top line and read from left to right; then proceed to the next line reading again from left to right as if reading a book.

Starting with the letter(s) at the top left of the call number books are ARRANGED ALPHABETICALLY:


A        AC        AG        AZ        B        BC        BT    

Books having the same letter(s) on the top line are all shelved together by the number group that follows the letter(s). THESE NUMBERS ARE ARRANGED NUMERICALLY, NOT DECIMALLY:

F        F         F         F         F        F         F
1        21        75        101       175      200       2113

When both the letter(s) and the number group that follows are the same, then books are shelved ALPHABETICALLY by the next letter:


 QM         QM        QM        QM        QM       QM      QM  
 23         23        23        23        23       23      23
 .A         .B        .C        .D        .E       .F      .G 

Books which are identical in first letter(s), in the number group that follows, and in the second letter, are then shelved by the next number group. THESE NUMBERS ARE ARRANGED DECIMALLY, NOT NUMERICALLY:


QM        QM        QM        QM        QM       QM       QM
23        23        23        23        23       23       23 
.E6543    .E778     .E88      .E9       .E99     .E995    .E999

Oftentimes a call number will have a fourth line which contains a letter and a number or numbers. THE LETTER IN THIS LINE IS ARRANGED ALPHABETICALLY, WHILE THE NUMBER(S) IS/(ARE) ARRANGED DECIMALLY.


QM       QM        QM        QM        QM        QM       QM
23       23        23        23        23        23       23
.E6543   .E778     .E88      .E9       .E99      .E995    .E999
A25      C6        F88       F885      F9        H92      K2

Note: The date of an edition frequently can be determined by its inclusion in the call number. However, the most accurate way of determining the edition date is to consult the information given in the preliminary pages of a particular volume.

Grateful acknowledgement is made to Gorgas Library, University of Alabama, Tuscaloosa, for granting permission to use this information developed at their institution.

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