Finding a Book on the Shelf--
Library of Congress Classification

The following shows you how to find a book with a Library of Congress (LC) Classification number. For an outline of the scheme see Library of Congress Classification Outline.

LC call numbers begin with letters of the alphabet. Each letter stands for a broad subject grouping; each letter and number that follow the first letter narrow down the subject. No two books have exactly the same call number. Numbers used in the following examples are hypothetical.

An example call number looks like this:

QA
349
.M613
W4
1993

The first line just needs to be treated alphabetically. Thus,

Line two is read in straight numerical order; numbers range from 1 to 9999 and are shelved accordingly:

Line three is often misunderstood. Line 3 is the Cutter number (named after Charles A. Cutter). It is a DECIMAL number, not a whole number like the second line. Therefore, .K79 comes before .K8. (There is usually a decimal point before the letter on that line, but even when the label does not show the point, line three is treated as a decimal number.)

Line four is called the Double Cutter number. It too is treated as a decimal number even though there is no decimal point showing:

Sometimes call numbers do not appear vertically, but horizontally.

Thus,

could appear as:

or even as:

R128 K8T43

Whether vertically or horizontally arranged, the Cutter number and Double Cutter numbers are always treated as decimal numbers.

One important thing to remember with call numbers is the rule, "nothing comes before something":

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A second way of describing call numbers follows. If you feel confident now, try to do the Call Number Exercises to test your knowledge. If you still have some questions, keep reading.

A call number is an address for a book or other material. In LC classification, numbers before the decimal point are read in ordinary numerical sequence, but after the decimal point, they are read decimally and not as whole numbers. The following represents how these books are arranged on the shelf:

Because there are two books with the same class number, SB 411, they are arranged by the number after the decimal point. To find a book on the shelf, look at each element of the call number.

Q	= Science	Single letters are filed before double letters in alphabetical order.
QA	= Math	Call numbers beginning with QA come AFTER those beginning with Q and BEFORE those beginning with QB.
QA 303	= Calculus	The second line is always a whole number that occasionally is followed by a decimal. The number 303 is actually three hundred three and would be shelved accordingly.
QA 303 .F	= Calculus book by Flanders	Once you find the QA 303's the call numbers are once again arranged alphabetically.
QA 303 .F56		Now comes the tricky part. The number following the .F is a decimal number, not a whole number. The number is .56 (not fifty six). This .F56 book would be shelved after QA 303 .F455 but before QA 303 .F6 (Or add the remaining decimal zeros: 560 is bigger than 455 and smaller than 600.) (This number is read as a decimal whether or not there is a decimal point.)

It may be helpful to think in terms of money: 45 1/2 cents is less than 56 cents which is less than 60 cents.

The following example of call numbers represents a shelf of literature books arranged in the order in which they appear on the shelves.

	P	PC	PC	PN
whole numbers	3	86	156.5	34
decimal numbers	.A86	.U6	.S48	.K7

	PR	PR	PS	PS
whole numbers	1990	1991.3	1629	1629
decimal numbers	.C5	.C3	.W35	.W4

Now try the Call Number Exercises.

How to do Library Research

Content: Naomi Lederer

Finding a Book on the Shelf-- Library of Congress Classification

Finding a Book on the Shelf--
Library of Congress Classification