A Guide to Understanding Library Call Numbers

The books and journals have spine labels with call numbers that are based on LCC (Library of Congress Classification). LCC is a system for assigning alphanumeric sequences that group similar books together and dissimilar books apart. This approach allows people to browse through the shelves and easily find materials on the same subject. Although assigning unique call numbers to all library materials is a complex skill, it's easy to learn the basics of reading a call number. The approach is always the same. For example, on third floor there're books with these call numbers:


※ Outline of LCC (Library of Congress Classification) System



LC # Subject LC # Subject
A General Works H Social Sciences
AP General Periodicals HA Statistics
B Philosophy--Religion HB-HJ Economics
B-BJ Philosophy HM-HX Sociology
BL-BX Religion J Political Science
C History--Auxiliary Sciences K Law
CB History of Civilization L Education
CT Biography M Music
D History (except American) N Fine Arts--Architecture
DA Great Britain P Language and Literature
DC France PA Classical languages and literature
DD Germany PB-PH Modern European languages
DK Russia PJ-PL Oriental languages and literature
DS Asia PM American and Artificial languages
DT Africa PN Literary history and collections
E-F History (American) PQ Romance literature
E American and United States (General) PR English literature
F United States (Local) PS American literature
G Geography--Anthropology--Sports PT Teutonic literature
LC # Subject LC # Subject
Q Science, General TC Hydraulic Engineering
QA Mathematics TD Sanitary & Municipal Engineering
QB Astronomy TE Highway engineering
QC Physics TF Railroad engineering
QD Chemistry TG Bridges and roofs
QE Geology TH Building construction
QH Natural history TJ Mechanical engineering & Machinery
QK Botany TK Electrical engineering & industries
QL Zoology TL Automotive & Aeronautical engineering
QM Human anatomy TN Mineral Industries: Mining, Metallurgy
QP Physiology TP Chemical Engineering & Technology
QR Bacteriology TR Photography
R Medicine TS Manufacturers: metal, lumber, paper
S Agriculture--Forestry TX Home Economics
T Technology (General) U-V Naval Science, Military Science
TA General & Civil Engineering Z Biliography, Library Science


TJ175.H34 1989

  1. A call number usually begins with one or two letters. The part of the classification system assigned to legal topics begins with three letters. A few areas of history also begin with three letters.
  2. The first letter "T" stands for "Technology." It's one of 21 main classes established by the United States Library of Congress. The first two letters "TJ" narrow the classification to the subclass "Mechanical Engineering and Machinery."

    A more detailed outline of the LCC (Library of Congress Classification) system is available at the Library of Congress.

  3. Numbers after the initial letters further define the subject of the book. In this case, TJ175 is a classification applied to books on "principles of mechanism &anp; kinematics of machinery."
  4. The second set of letters and numbers in the call number usually represent the author or title of the book. In this case, the H34 in TJ175.H34 refers to Edward J. Haug, who's the author of the book "Computer Aided Kinematics and Dynamics of Mechanical Systems." In some parts of the LCC system, the second set of letters and numbers represents a further refinement of the subject. For these call numbers, the third set of letters and numbers represents the book's author or title.
  5. Books and journals are shelved in call number order.

The letters at the beginning of the call number are used to shelve books in alphabetical order.

※ example : QA







If two books have the same initial letter(s), then the succeeding numbers are used to place the books in numerical order.

※ example : TJ5






The call number's second alphanumeric sequence is preceded by a decimal point. The numbers that follow are treated as a fraction. This part of the call number places books in decimal order.

※ example : TJ173 .C6
TJ173 .C65
TJ173 .C657
TJ173 .C7
TJ175 .D48






The end of a call number may include the publication year, volume number, or copy number.

※ example :

TJ175 .H34
TJ175 .M123 1975
TJ175 .M123 1978
TK781.67 .M53 .L48 1996