Guide to Understanding Library Call Numbers

What Are Call Numbers For?

Have you ever wondered how library books are assigned their places on the shelves? Did you know that the call number -- the number placed on the spine of the book -- is a code which provides valuable information about the book? This page will provide an introduction to understanding and using library 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.

Example of a Call number:

Call number example

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

Seneca College Libraries, like many other academic libraries in Canada and the U.S. use Library of Congress Classification for call numbers. This system uses a combination of letters and numbers to arrange materials by subjects.

Reading Call Numbers

Call number example 2 Read the call number line by line:
Read the first line in alphabetical order:
Read the second line as a whole number:
The third line is a combination of a letter and numbers.
Read the letter alphabetically.
Read the number as a decimal, cg: .C65=.65
Some call numbers have more than one combination letter-number line.
This is the year the book was published.
Chronological order: 1985, 1987, 1991...

Putting Call Numbers in Shelf Order

To understand how call numbers are put in order in Library of Congress Classification, again look at each section of the call number.

Classification diagram

What Does the Call Number Mean?

Remember that Library of Congress Classification arranges materials by subject. The first section of the call number represents the subject of the book. The letter-and-decimal section of the call number often represents the author's last name. And, as you probably recall, the last section of a call number is often the date of publication.

Classification diagram 2

Why is this important to know?

Because books are classified by subject, you can often find several helpful books on the same shelf, or nearby. For example, within the same call number LB2395, there are other guides for college study.

Since Library of Congress Classification arranges materials by subject, knowing the letter(s) for your subject area gives you a place to start browsing the shelves. Which letters represent your subject?

Location Prefixes

When a call number looks like the example above, (e.g. LB2395 .C65 1991), the book is shelved in the General Collection. Some call numbers, however, are preceded by a location prefix.

Example: REF AG243 .G87 1992 -- The REF prefix indicates that this book is shelved in the Reference Collection.

Location prefixes mean that book is shelved in a special place, and may have loan restrictions.