LIBRARY OF CONGRESS CALL NUMBERS

Library of Congress call numbers are made up of at least three lines:

• The first line is a letter or letters and it is arranged in alphabetical order.
• The second line is a whole number and it is arranged in normal numerical order.
• The third line is a combination of a letter and number. This line is arranged alphabetically and then by decimal number.
• Sometimes there is an additional line with a letter-number combination (which is arranged in the same way as the third line) and sometimes there is a publication year on the bottom line of the call number.

For example, here is a typical LC call number:

QB 44 M65

Before we discuss how to find the book with this call number, look on the LC classification chart to find the subject of any book with a call number starting with QB. You should find that a call number beginning with QB means that the subject of the book will be related to Astronomy.

To find the book with this call number on the shelf, you would first look for the shelves with books with call numbers starting with Q. Books are arranged on the shelves by call number beginnning with books with call numbers starting with A and ending with books with call numbers starting with Z. At the end of each set of shelves are labels identifying the call numbers of the books on those shelves.

The order of different call numbers is determined by comparing each line of each call number starting from the top and then going down until you find a difference between them. If the first lines of two call numbers are the same, check the second lines. If both the first and second lines are the same, compare the third lines; and so on.

Continuing with our example, once you find the books with call numbers starting with Q, follow the call numbers of the books and you will then see books with call numbers starting with QA and then books with call numbers starting with QB. Thus, call numbers are arranged first by the letter or letters on the first line in alphabetical order.

Q 771 .H37

Q 850 C125

QA 52 .M15

QA 418 .J32

QA 2645 L433

QB 44 M65

QC 227 F22

Let's continue to look for the call number in our example:

QB 44 M65

Once you find the call numbers starting with QB, look at the numbers on the second row of the call number. Follow them numerically until you find 44. The second line of an LC call number is arranged numerically.

Now you've found the books that start with:

QB 44

If there is only one book that has a call number beginning with those two lines, you don't have to look any farther to figure out the order. When you find many call numbers with the same first two lines, however, you need to compare the third lines of each one. Understanding the order of the third line, with the letter-number combination (M65, in our example) can be a little confusing. The combination is read first alphabetically by letter and then numerically by the number. The tricky part is that the number is a decimal number.

First find the letter (M, in our example) alphabetically. If all of the letters are different, the order is decided just by the letters. If there are any call numbers with the same first two lines and with the same letter at the beginning of the third line, you then have to compare the numbers following the letter.

The number after the letter (65, in the example) is a decimal number. This is where many people get confused. Look closely at the following call numbers which are in correct order:

QB 44 .H37

QB 44 M125

QB 44 .M15

QB 44 .M3

QB 44 M6188

QB 44 M65

QB 44 R22

If you remember that the numbers in the third row after the letter are decimal numbers, the order will make sense. If you have trouble with decimal numbers, remember that there are imaginary zeros at the end of all decimal numbers. So in the example, you can see why M125 comes before M15 if you put a zero after the 15. Another way to understand this is to look at one number at a time. For example, the first number in both M125 and M15 is 1, but the second number in M125, which is 2, comes before the second number in M15, which is 5.

A decimal point may be included at the beginning of the third line (as in .H27, .M15 and .M3 above) but, whether or not a decimal point is included, the order is the same.

If there is a fourth line with a letter-number combination (and all previous lines of multiple call numbers are the same), that line would be arranged in the same way as the third line. For example:

QB 44 M3 R2485

QB 44 M3 R535

QB 44 M3 R59

Look at the following examples of correct call number order. Be sure that you understand why they are in the order shown. If you do not understand, be sure to ask a librarian to explain it to you.

B 778 F1544 T22 1996	B 5545 R28	B 5545 .R7 1993	E 88 G2512 S57 1998	E 88 G62 D225	E 88 .G62 L166 1995	E 88 G62 L45
F 774 R28 W2548 1990	F 774 .R28 W486	F 774 R28 W73 1989	F 5833 D27 1992	F 5833 D5 E42	F 5833 M76 E31	F 5833 .M76 E5
Q 2285 F387	QA 333 G2591 L62	QA 333 .G2591 L7	QA 333 G437 D32 1994	QA 333 .G55 M84	QA 2141 .B38 R5	QA 2141 B7 F48

For another explanation of Library of Congress Call Numbers, check out
Hawaii Community College's "Understanding Call Numbers" web page.
(Disregard the information on "Location Prefixes" at the end of the page.)

TAKE A PRACTICE QUIZ:
To be sure you understand call number order, try the call number quiz at: http://www.wcsu.ctstateu.edu/library/lc_quiz.html

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These materials may be used for educational purposes if you inform and credit the author and cite the source as: LSCI 105 Online Research. All commercial rights are reserved. To contact the author, send comments or suggestions to: Eric Brenner at brenner@smcccd.cc.ca.us