Understanding Call Numbers

What are call numbers for?

Each book in the library has a unique call number. A call number is like an address: it tells us where the book is located in the library.  Call numbers appear 

Call numbers on the spines of books and in the online catalog
Note that the same call number can be written from
top-to-bottom, or left-to-right. 

Alvernia College Library uses the Dewey Decimal System for call numbers. This system uses a combination of numbers and letters to arrange materials by subjects.


What do the parts of a call number mean?

Call numbers are basically divided into two parts:

  • subject classification: series of numbers that represent the subject area
  • author classification: series of letters and/or numbers that represent the author or title of the information

Some call numbers have a third part for the year of publication or extra author information.

Let's look at how we can interpret the call numbers of the book The Fly in the Cathedral by Brian Cathcart. The call number for this book is:

  • The first number, 5, indicates the book is in the 500s, which is the field of natural sciences and mathematics
  • The second number, 3, places the book in the 530s, which is the field of physics
  • The third number, 9, places the book in modern physics
  • The fourth number, .7, indicates the book is about atomic and nuclear physics
  • The second line, C362, refers to the author Cathcart. Each author is assigned a unique number.
  • The third line, 2005, tells us the publication date

The meaning of the call numbers illustrates how items about similiar topics are grouped together on library shelves. When you find a book on your topic, check the books on the same shelf; you may find additional relevant books.

How do I use a call number to find an item?

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It is important to note the entire call number. Then you need to find each part of the number in turn.

For example to find the book A short history of Ireland, by Richard Killeen with the call number

  1. Locate the first three digits
  2. Locate any digits following the decimal point. Remember that it is a decimal system, so 941.7081 comes after 941.68
  3. When you have located the number in full, look for the letter, then the next set of numbers
  4. Check that the last letter and number are correct, to make sure you have the right book and edition



  • items on the same topic are shelved together
  • every part of the number is important for locating an item
  • work through the call number systematically to find the item