Dewey Decimal System

The Dewey Decimal System is one system of library organization. While most academic libraries use Library of Congress Classifications, Pratt Institute Libraries retained the Dewey Decimal System from its time as a public library.

The global library cooperative OCLC provides the following thorough resources for librarians organizing library materials with the Dewey Decimal System:

• A summary of the Dewey Decimal System including: the history of the Dewey Decimal System, guides to reading Dewey call numbers, and organizational classes.
• A PowerPoint further explaining the Dewey Decimal System.
• OCLC provides further resources for Dewey catalogers, including The Dewey Blog.

NYPL created this simple guide to subject call numbers and popular subdivision.

How to Read a Dewey Call Number

This page from our Pratt Library How-To Guide zine illustrates how to read a call number:

Dewey Decimal call numbers are organized as follows:

• Before the decimal, books are organized in ascending numerical order from 000-999. These three numbers are the Main Class, organized broadly by the subject of the book.
• Books are also organized in ascending order after the decimal; for instance, a book with the call number 700 (no decimal) would precede 700.01, with 700.10 further along the shelf. Numbers after the decimal are subdivisions of the Main Class, organized further by subject and author.
• After the number sequence, a letter and number sequence should be first read alphabetically, then numerically in ascending order. So 700.01 A123 would precede 700.01 B231.

This guide provides a more thorough primer on reading Dewey Decimal call numbers. Additionally, the HowCast video below succinctly explains Dewey Decimal call numbers:

But Where are the Letters?

It's likely that if you spent time in another academic library you grew accustomed to finding your favorite section by remembering a call number that started with letters, like NA190 for books about the history of architecture. That library organization system is the Library of Congress Classification System. If you know your LOC faves, this guide will help you translate Library of Congress call numbers into Dewey.

Conversely, you may be preparing to visit another library - like the Watson Library at The Met - and want to use your Dewey Decimal knowledge to quickly find books in a Library of Congress system. This guide translates Dewey Decimal into the Library of Congress call numbers for easy browsing.