EA Research

Understanding Call Numbers

To be able to efficiently read Library of Congress (LC) call numbers is quite a skill. This tutorial was created to help library users uncover the mysteries of call number reading.

Let's start with a sample call number:

QE534.2.B64

Call numbers can begin with one, two, or three letters.

• The first letter of a call number represents one of the 21 major divisions of the LC System. In the example, the subject "Q" is Science.
• The second letter "E" represents a subdivision of the sciences, Geology. All books in the QE's are primarily about Geology.
  • Books in categories E, United States History, and F, Local U.S. History and American History, do not have a second letter (exception: in Canada, FC is used for Canadian history).
  • Books about Law, K's, can have three letters, such as KFH, Law of Hawaii. Some areas of history (D) also have three-letter call numbers.
• Most other subject areas will have call numbers beginning with one or two letters.
  • For most of the subject areas, the single letter represents books of a general nature for that subject area (i.e. Q - General Science or D - General World History).

Numbers after letters.

• The first set of numbers in a call number help to define a book's subject.
• "534.2" in the example teaches us more about the book's subject. The range QE 500-625 are books about "Dyamic and Structural Geology."
• Books with call numbers QE534.2 are specifically "Earthquakes, Seismology - General Works - 1970 to Present"
• One of the most frequently used number in call numbers is "1" which is often used for general periodicals in a given subject area.
  • For example, Q1.S3 is the call number for the journal Science.
• Journals are also given call numbers based on the specific subject.
  • For example, QE531.E32 is the call number for the journal Earthquake Spectra as QE531 is the call number for periodicals about "Earthquakes, Seismology"

Cutter Number

• The cutter number is a coded representation of the author or organization's name or the title of the work (also known as the "Main Entry" in library-lingo).
• Charles Ammi Cutter first developed cutter numbers using a two-number table.
  • A three-number table was developed in 1969.
• In our above example, QE534.2.B64, the B64 is taken from the two-number table and represents the author's last name, Bruce A. Bolt.
  • The book is Earthquakes.
• Some books have two Cutters, the first one is usually a further breakdown of the subject matter.
  • For example, QA 76.76 H94 M88 is a book located in the Mathematics section of the Q's.
    • QA 76 is about Computer Science.
    • The ".76" indicates Special Topics in Automation.
    • "H94" tells us that this is a book about HTML.
    • "M88" represents the last name of the first author listed's last name, Musciano.
    • The book is HTML: The Definitive Guide

Shelving and Locating

Items are shelved by call numbers - in both alphabetical and numerical order. The letters at the beginning of the call number are alphabetical. The numbers immediately following are in basic numerical order, i.e. 5 then 6, 50 is after 49 and before 51, and 100 is after 99. Thus,

The cutter numbers (A3, A31, Z4, C3, and A2 in the above example) are sorted first by the letter and then by the number as a decimal. For QD 1 A5 think of it as being QD 1 A 0.5, for QD 1 A332 read QD 1 A 0.332. Therefore,

Dates, volume and issue numbers, copy numbers, and other annotations are like an additional cutter number but are shelved by basic alphabetization (numbers alone come before letters):