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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,

A3 A31 Z 4 C 3 A 2

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.

A 3 A 31 A 311 A 4 A 41 A 415 A 42

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):

Q 10 Q 10 Q 10 Q 10 Q 10 AD 1 AD 1 AD 1 AD 1
C 3 C 3 C 3 C 3 C 3 A 5 A 5 A 5 A 5
  1993 1990




copy 2

vol 1 vol 2

vol 2


Vol 2




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