How to Read Call Numbers

Sullivan Family Library uses the Library of Congress classification system. This system arranges materials by subject using a combination of letters and numbers. Read call numbers line by line, from left to right, and from top to bottom.

The first line of a call number begins with one or two letters. These letters are read alphabetically:

Q

before

QC

before

QH

The second line is made of a number that may have one or more digits. This line is read numerically, as a whole number:

QB
160

before

QB
853

before

QB
853.35

The third line is the trickiest part of the call number! The letter is shelved alphabetically, and the number following the letter is treated as if it were preceded by a decimal:

QB
841
.C45

before

QB
841
.C456

before

QB
841
.C47

Sometimes, a call number will have a fourth line, to further delineate a book from similar books. It is read the same way as the third line, the letter alphabetically and the number as a decimal, even though it is often not preceded by the decimal point.

QB
841
.C45
M151

before

QB
841
.C456
P90

before

QB
841
.C47
H23

The final lines of the call number may include dates and other annotations. These annotations are read after the call number.

QB
841
.C45
M151
2000

before

QB
841
.C456
P90
1999

before

QB
841
.C47
H23
2004
c. 2

Adapted from the Stan Getz Library