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What are call numbers?

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.

We use the Library of Congress Classification system for our call numbers (except in the Education Curriculum Collection which uses the Dewey Decimal Classification system). This classification system arranges books according to what they are about, so that books on the same topic are shelved together.

Image with the following text: Tip: Since books on the same topic are shelved together, be sure to browse the area where you find your book(s), as you’ll also find other books on the same topic!

Books are shelved in call number order and call numbers are 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. Call numbers appear differently in the online catalogue than on books—in the catalogue, the entire call number is in one row; on books, they are split into multiple rows to fit on book spines:

Image with the following text: Call number as displayed in the library catalog: BS 680 .W6 E56 2019. All the text is in one row.Image with the following text: Call number on label on book spine: row 1: BS; row 2: 680; row 3: .W6; row 4: E56; row 5: 2019.

Call numbers are easiest to understand if you break them into their parts.

Start with the Letters

Image with sample call number on 5 rows: row 1 is highlighted in yellow: BS; row 2: 680; row 3: .W6; row 4: E56; row 5: 2019.

Call numbers start with 1, 2, or 3 letters, indicate a book's broad subject area, and are arranged alphabetically. Single letters come before double and triple letters:

. . . B, BL, BR, BS, BT, BV, BX . . . K, KB, KC, KJ, KJA, KJC, KL, KLA, KM . . . 


Next, the Number

Image with sample call number on 5 rows: row 1: BS; row 2 is highlighted in yellow: 680; row 3: .W6; row 4: E56; row 5: 2019.

Following the letters is a 1-4 digit number which further defines the subject of an item. These numbers may be followed by a decimal point and additional digits, for example:

320.3, 708, 1605.53, 4832.2

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, 1253, 2756

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

Image with the following text: Tip: 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 is the same as 73.000; 73.1 is the same as 73.100; 73.16 is the same as 73.160; 73.2 is the same as 73.200; 73.351 is the same as 73.351; 73.36 is the same as 73.360; 73.5 is the same as 73.500

The Letter-Number Groups (Cutter Numbers)

Image with sample call number on 5 rows: row 1: BS; row 2: 680; row 3 is highlighted in yellow: .W6; row 4 is highlighted in yellow: E56; row 5: 2019.

Next come 1 or 2 letter-number groups consisting of a single letter and a number with 1-4 digits. Usually only the first group is shown with a decimal point in front of it, but both are read the same way—first alphabetically 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.

Image with the following text: Trivia: These letter/number groups are called Cutter Numbers, named after the person who invented them.

Image with the following text: List of call numbers: BX 6700 .B6 V3; BX 6700 .C49 T4813; BX 6700 .C49 T6; BX 6700 .C5 L5; BX 6700 .C55 G32; BX 6700 .C7 R73; BX 6700 .E3 N52. In this example, all seven of these call numbers start with BX 6700, so we move on to the first Cutter number and compare them. B comes first, followed by C, then E. For the 5 that start with C, we put them in numerical order: .49, .49, .50, .55, .70. For the 2 that start with BX 6700 .C49, we then compare the second Cutter number to determine order.

Image with the following text: Note: The last letter/number group is usually based on the last name of the book’s author. Books on the same topic are usually shelved in order of the authors’ last names.

Year of Publication

Image with sample call number on 5 rows: row 1: BS; row 2: 680; row 3: .W6; row 4: E56; row 5 is highlighted in yellow: 2019.

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




Other Information You Might See in Call Numbers

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). These differences will not affect the way the call number is read or the way the book is shelved.

The call number label on the book sometimes also includes a copy or volume number at the bottom:

c.2 (copy 2)

v.12 (volume 12)

Call Numbers at Ambrose Library

If you're interested in browsing a particular subject area, you may want to consult the document below; it lists all the Library of Congress classification numbers that are available at Ambrose Library.