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Call Numbers (How to Read Them): Learn About Call Numbers

A guide to call numbers designed and created by Clark Librarians

Learn About Call Numbers

image of a frustrated man standing in a pile of books thinking "please pinch me and wake me up"Where's that Book?

What would you do if you walked into the library and all the books were piled all over the place?

Just joking. Libraries label and organize stuff so you don't have to spend hours looking for what you need.

If you understand the system a little, you'll be able to find books quicker and easier. If you understand it well, you can let the system lead you to more books on your topic.

Stacking Up Systems

Know which one your library uses.

Libraries put books on shelves, called stacks, where books on the same subject next to each other. For example, books about gardening sit next to each other, books by Shakespeare are together, and books about car repair are together.

To keep track of all the subjects, libraries use a classification system. There are two main classification systems:

  • The Library of Congress System is used by most university and some college libraries. Clark College Libraries use the Library of Congress system
  • The Dewey Decimal System is used by public libraries and some college libraries.

Both of these systems use call numbers to identify individual books. Call numbers are printed on labels and attached to each book in the library.

Like snowflakes, no two call numbers are alike. Each one is unique to a specific book.

image of a call number on a label on the spine of a book

Library of Congress Call Numbers

Used by academic and research libraries

Let's say you are looking for the book called Guts: Companies that Blow the Doors off Business as Usual.

Search the title in the library catalog to find the call number:

screen capture of a library catalog record


Call numbers are arranged using an alphanumeric system, meaning you follow both alphabetic and numeric order to find books.

On the shelves you would find call numbers that start with H, then HD, then HD57, then HD 57.1... and so on, until you zoom in on the book you want.

The first letters in a call number also stand for the main subject of the book.

The graphic illustrates how to read a call number from top to bottom.

graphic describing the what the parts of a call number stand for.

Dewey Decimal System

The Dewey Decimal system is used by public libraries, K12 libraries, and some college libraries.


Suppose you're looking for the same book, Guts: Companies that Blow the Doors off Business as Usual in a library that uses the Dewey Decimal System.

Search the title in the book catalog to find the call number:

screen shot  showing the Dewey Decimal call number for the book 658.4092 F862g 2004

Call numbers are arranged using a numeric and alphabetic order.

First find the number on the shelf, then get the specific location using the letter. 

The first numbers in a call number also stand for the main subject of the book.

Here's an example of what the letters and numbers stand for in the sample book.

graphic showing what the lines in a call number stand for.


Call Number Main Classes

Side-by-side comparison

The charts on this page show the very broadest level of the codes, or main classes, that call numbers start with.

Don't worry about memorizing these. Your library has posters and flyers to remind you what the codes stand for.

The great thing about both systems is that once you find one book on your topic, other books on the same topic or similar topics will be in the same area. So browse away!

chart comparing Library of Congress and Dewey Decimal main classes

Taking a Field Trip?

You'll appreciate the uniformity

You've learned that most libraries across the country use either Dewey or LC to organize their books. Here's another useful thing to know: most libraries buy their call numbers from the same company.

So, if you find a book in one library that uses the Library of Congress system, chances are that the call number would be the same (or very close to the same) in another library using LC. The same is true for libraries using Dewey Decimal.


Title of Book: The Starbucks Experience: 5 Principles for Turning Ordinary into Extraordinary

Library Call Number
Clark College Library HD9199.U54 S736 2007
Bellevue Community College Library HD9199.U54 S736 2007
North Seattle Community College Library HD9199.U54 S736 2007
Pierce College Library HD9199.U54 S736 2007
... see how it works?


In larger or smaller libraries you might find minor differences, but in general, the uniformity makes it easy for you to find materials and be comfortable using different libraries.

Sometimes There are Many Different Subjects in the Same Book

Call numbers can focus a subject.

You've learned that the first line of call numbers represents the general subject of the book. But often subjects are linked with other subjects. Like Art and Music, or Gaming and Education. Libraries choose the main subject so that books on a similar topic are next to each other. Examples:

Using Library of Congress, if the topic is leadership ...

  • leadership in business starts with HD
  • leadership for lawyers starts with KF
  • leadership for politics starts with JK
  • leadership for school principals starts with LB


Using Dewey Decimal, if your topic is leadership ...

  • leadership in business starts with 658
  • leadership for lawyers starts with 347
  • leadership for politicians starts with 320
  • leadership for principals starts with 371

Finding books with many subjects

If a book has three, four, or more subjects, will the library buy many copies to have one copy for each subject call number?

Of course not. Keeping track of multiple subjects is the job of the library catalog -- the database you use to locate library materials. The physical book can only be on one place, but the electronic record for the book can include references to all the subjects in the book. The library catalog is the best tool to start your search for library materials.

Let's Summarize

The Most important points

  • Libraries use call numbers to organize books on the shelves.
  • Two main call number systems are Library of Congress Classification, and Dewey Decimal.
  • Call numbers are read left to right, line by line, following the alphanumeric (alphabetical and numerical) rules.
  • In both LC and Dewey, the first line represents the subject of the book.
  • Once you find one book on your topic, you can browse near that book to find others books on the same or similar topic.
  • The best tool for locating call numbers is the library's book catalog.


image of a happy man looking at books on the shelves, caption is "it's all about finding information"


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