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Understanding Library of Congress Call Numbers

This guide explains how to read Library of Congress call numbers to locate books in the stacks.

How to Find a Book in the Stacks

Once you have the call number you need to know on which floor of the library the book is shelved. Consult the library's Floorplans to see where materials are shelved. The floorplans reveal that all Reference books are on the first floor. Circulating books with call numbers A-PN are on the second floor and books with call numbers PN-Z are on the third floor. So this book should be on the third floor of Buley Library because the call number begins with the letters PR.

When you go to the third floor you need to look for the PR section. This is a large section and you need to know how to read the call number in order to locate the book. (Single letters are filed before double letters so you will see books with the letter P first, then books beginning with PA, PC, PE, PF, PQ, etc.).

This is how the call number will appear on the spine of the book:


Read call numbers line by line.
Read the first line in alphabetical order: A, BF, LB, M, ML, P, PE, PQ, PR, QR, RT, Z .........
Read the second line as a whole number: 1, 2, 3, 36, 78, 78.62, 100, 110, 135.5, 1000, 2000, 2530 .......(A call number with a smaller number comes before a call number with a larger number so 32.5 will come before 33 and 66.18 will come before 66.2)
The third line is a combination of a letter and numbers. (Some call numbers may have more than one letter-number line)
Read the letter alphabetically.
Read the number as a decimal. Example:   .S24 = .24; .P633 = .633
The last line is the year of publication (1999)