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Using the Library

How to Read Call Numbers

We use the Library of Congress Classification system for our call numbers. The classification system arranges our books according to what they are about, so that books on the same topic are shelved together. Books are shelved in call number order, so you can find a specific book when you need it.

Call number as displayed in the library catalog:
QA76.774.L46 S65 2013
Call number label
Label on book spine

Call numbers are actually made up of letters and numbers that follow a pattern: a letter or letters, followed by a number, followed by one or two letter-number groups, followed by the year of publication. It's easiest if you break the call number into parts.

Start with the Letters


Call numbers start with one, two, or three letters, and are arranged alphabetically. Within each letter, single letters come before double and triple letters:

. . . B, BC, BD . . . K, KB, KC, KJ, KJA, KJC, KL, KLA, KM . . .

Next, the Number


Following the letters is a 1–4 digit number, which may be followed by a decimal point and additional digits.

Examples: AE5, TP369, G2898.2

To the left of the decimal point, the number is treated like a regular number, in that single-digit numbers come before two-digit numbers, two-digit numbers before three-digit numbers, etc. 

1, 3, 10, 23, 76, 145, 312, 760, 2756, 5790

If the number has a decimal point, you then compare the digits to the right of the decimal point from left to right, to figure out what comes next.

73, 73.1, 73.16, 73.2, 73.351, 73.36, 73.5

Hint: Many people find it helpful to imagine extra zeros to the right side of the number so that you are comparing numbers with the same number of digits.

  • 73
  • 73.1
  • 73.16
  • 73.2
  • 73.351
  • 73.36
  • 73.5
is the same as
  • 73.000
  • 73.100
  • 73.160
  • 73.200
  • 73.351
  • 73.360
  • 73.500

The Letter-Number Groups (Cutter Numbers)



Next comes one or two letter-number groups consisting of a single letter and a number with one or more digits. Usually only the first group is shown with a decimal point in front of it, but both are read the same way – first by the letter, then by the number as if there was a decimal point to the left of it, as described in the section above.

Trivia: These letter-number groups are called Cutter numbers, named for the guy who invented them.
  • PX2.B6 V3
  • PX2.C49 T448
  • PX2.C49 T6
  • PX2.C5 L5
  • PX2.C55 G32
  • PX2.C7 R73
  • PX2.E3 N52
In this example, all seven of these call numbers start with PX2, so we move on to the first Cutter number and compare them. B comes first, followed by C, then E. For the five that start with C, we put them in numerical order: .49, .49, .50, .55, .70. For the two that start with PX2.C49, we then compare the second Cutter number to determine order. 
Good to Know: The last letter-number group is usually based on the last name of the book's author. Books on the same topic, therefore, are usually shelved in order of the authors' last names.

Year of Publication

The call number often ends with the year the book was published.

Other Things You Might See

You might occasionally see something in a call number that isn't described above. But you should still be able to figure out where to find it using the same principles.

You might notice slight differences in the way a call number is shown on a computer screen (such as with spaces between parts of the call number) or on a book label (such as where parts of the call number are broken to the next line). But these will not affect the way you read the number..

The call number label on the book sometimes also has a volume or copy number printed on it.

More Examples

  • F2131 .D85 1989
  • G7 .N271
  • G50.212 .W57 2012
  • G419.M2 P37 2003
  • GC21 .C3 1961
  • GF13 .E47 2008
  • GF21 .C37 1999
  • H61 .C24 1988
We start by comparing the letters, which puts F2131 first and H61 last. Within each letter, single letters come first, and the three call numbers that start with a single G are placed in order by their numbers. GC is next alphabetically, and is followed by the two GFs in numerical order, GF13 and GF21.


  • DU627.B57 P21 2014
  • DU627.B6 G3 2006
  • DU627.C4 E55 1994
  • DU627.73.D21 B78 2007
  • DU627.73.D21 K24 1998
  • DU627.735.C24 H12 1997
  • DU627.74.A2 K24 1996
  • DU627.8.R3 H2 1991

All of these are the same up until the first decimal point, so we start from there. Past the decimal point, we follow the rule of comparing numbers from left to right.

The three call numbers that don't have a number to the right of the decimal point come first. You can think of them as being the same as DU627.0 if it helps.


How to Find a Book on the Shelf

First, Use the Library Catalog to Find the Call Number

Use the Primo system to search the library catalog for books and other materials in the library's collections. It will give you the call number, as well as other information about the book's location and availability.

online library catalog showing call number and other details

Check to make sure that the book you are interested in is owned by the Leeward CC Library, as our library catalog might (depending on the search options you choose) show you information about books owned by other libraries in the University of Hawaiʻi system.

In our library, our books are divided up into different collections, located in different parts of the library. Most of our books are in the General Collection. But many are in the Reference Collection, the Hawaiʻi-Pacific Collection, the Hawaiʻi-Pacific Resource Room, and other locations.

Then, Go to the Bookshelves

Go to the collection that has the book you want . See the library map to see where our collections are.

Collections are arranged in a continuous A-to-Z sequence in the order described in the section above. Look for signs on the ends of the bookshelves that tell you what range of call numbers is on each row of shelves.

Books are arranged left to right on the shelf, and top to bottom in a column of shelves.

Books have a call number label, usually near the bottom of the spine. Thin books have the label on the front cover, so you'll have to pull the book off the shelf a little bit to see it.


Hints: Remember that call numbers can start with one letter, two letters, or sometimes three letters. If you're looking for a call number that starts with two letters, and you see books with one-letter call numbers on the shelf in front of you, take a few steps to your right and look there.

Also remember that the number after the letters and before the decimal point can have one, two, three, or four digits. So if you're looking for a call number with a 4-digit number and you're seeing 3-digit numbers on the shelf in front of you, go farther to your right until you see 4-digit numbers.

Call Number FAQs

Why is it called a "call number" anyway?

Some libraries are "closed shelf", meaning they don't let the public into the room where the books are kept. The call number was what was "called" back to the staff member who retrieved books that were requested.

Is this like the Dewey Decimal System?

It does the same thing. Dewey Decimal Classification is commonly used in public and K-12 school libraries. It covers a very broad range of topics, but doesn't go very deeply into specialized topics. Library of Congress Classification is used in most college and university libraries. If focuses on topics of scholarly research, and addresses very specialized topics within those areas of focus.

Why is your system so hard to use?

The Library of Congress is a closed-shelf library, where trained staff retrieve the books. Their system focuses on precise classification of specialized works, rather than making it easy to find something on the shelf.