How do I read a call number?

A call number is like a book’s address in the library. It helps you find the book on the shelves.

At PSU, Dewey Decimal numbers are used to organize books by subject. Cutter numbers identify the author, and the publication year helps distinguish editions. Here's how to read it:

The call number starts with a Dewey Decimal number, which represents the main subject area. The Dewey system uses numbers from 000 to 999 to organize books into broad categories. For example:

• 300 = Social sciences

• 510 = Mathematics




• 920 = Biography

Here's the full list

After the Dewey number, there may be additional decimal numbers to narrow down the topic. For example:

• 320.973: Political science in the United States.

• 513.2: Elementary geometry.

After the Dewey number (and decimal number), you may see a Cutter number, which represents the author or a part of the title. It’s usually a combination of letters and numbers. For example:

• 320.973 M621: A book on U.S. political science by an author whose last name starts with "M"

Finally, the year of publication may be included to further specify the book, especially if there are multiple editions. For example:

• 320.973 M621 2005: The same book, published in 2005.

320.973 M621 2005

• 320: Political science.

• .973: Specific to the U.S.

• M621: Author’s Cutter number.

• 2005: Publication year.