How to Read a Call Number


Most of our materials are organized on the shelf into groupings of similar subjects using the Library of Congress Classification System.

Each book is given a unique identification number (or call number) which is found on the spine of the book.

Study skills for psychology students
By Jennifer Latto

Line 1 and Line 2 describe the subject of the book.
BF 77 = Studying and teaching

Line 3 often represents the author's last name.
L = Latto

Line 4 is usually a date and represents the year of publication.

To read the call number on the book spine, look at one line at a time.

  • Line 1: BF
  • Line 2: 77
  • Line 3: .L28
  • Line 4: 2009

Start with line 1

Books are arranged on the shelves in alphabetical order by the letters on the first line of the call number.

For example, first come all the B call numbers, then all the BD call numbers, then BE, etc.

Simple diagram showing sequence of letters from the first line of the call number.

Look at line 2

Within the BF call numbers, books are arranged in numerical order from low to high.

Simple diagram showing sequence of numbers from the second line of the call number.

Move to Line 3

Line 3 of the call number has a letter and a number. The line is first sorted alphabetically by the letter.

Once you find the letter, then read the number. But note (whether there is a period shown or not) these are all decimals not whole numbers.

Example: B39 is read as B .39. This is why B3593 comes before B39 (B .3, B .39, B .4).

Simple diagram showing sequence of numbers from the third line of the call number.

Line 4

Most books will display a fourth line which is usually the year of publication, but in some cases might indicate a volume or multiple copies of the book. 

The fourth line is not needed to locate the book on the shelf. It is more informational or useful when there are several editions of one title.

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