DCPLive is a blog by library staff at the DeKalb County Public Library!
Mar 25 2008

Library Basics: The Dewey Decimal System

by Chris S

After working in a public library for nearly six years, it still strikes me the number of library users who are mystified by all those little numbers on our nonfiction books’ spine labels.  The Dewey Decimal Classification System (DDC) was invented by American library pioneer Melvil Dewey, a very odd but brilliant scholar and reformer.  Aside from his successful classification system and role in founding the American Library Association and the magazine Library Journal, Dewey was also a proponent of spelling reform, and attempted to change his birth name, “Melville Dewey” to “Melvil Dui” (only the first name’s spelling stuck).  His legacy to us, the public library users of the world, is a simple and effective system of classifying all human knowledge.  Here’s how it works:

Three Digits to Left, Up to Four Digits on the Right, or 364.1523 = True Crime

Every nonfiction book is assigned a number, known as a “call number.”  The three-digit number to the left of the decimal is associated with a certain subject.  For example, “005” is for computer programs, and “641” is for cooking (or “cookery” as the subject heading is known).  The numbers to the right of the decimal refine the subject, and allow you to get more specific about what type of computer program (“005.369” is where you would find Microsoft Office programs) or cooking (“641.595” is where you would find Chinese cookbooks).  Different library systems allow more decimal digits, which means you can further pinpoint what you’re searching for.  DCPL goes out to four digits, which works well for our needs.

What About the Letters Underneath?  or What does “Chi” mean?

While the call number gets you to the right subject area, some sections are so big that you need a little more information to get you to the exact book you’re looking for.  Let’s say you’re looking for The Way to Cook by Julia Child, and when you check the catalog, you just write down the number “641.5” and run to the shelf.  You would find that there are many (perhaps a hundred or more) titles filed under this number.  When you go back to the catalog you see that the full call number is “641.5 Chi.”  Yep, you guessed it – “Chi” is for “Child,” the first three letters of the author’s last name.  Lucky for you, we library staffers keep those letters in alphabetical order so that you can quickly find what you’re looking for.

Okay, Lets Review:

When you go to the catalog and find a specific call number (like 641.5 Chi), or you ask a staff member where cookbooks are and they tell you “in the 641s,” here’s how you find it:

  1. Find the three digit number to the left of the decimal (like 641).  The numbers are all in order from 001 to 999, so this part will be easy.
  2. Once you’re in the 641s, look at the numbers to the right of the decimal (also in order – 641.1, 641.2, etc.) until you find what you’re looking for.
  3. Once you’ve found the right number area, start looking for the letters, which are also filed alphabetically.

Voila!  You’ve found your book!  Happy searching!

Further Reading

Okay, if you’re actually interested in further reading about this, here’s a link to ways to begin a career in libraries!  For the simply curious, here are some good sources for Dewey Decimal information:

How to Use the Dewey Decimal System – a basic overview provided by the Monroe County (Indiana) Public Library.

Dewey Decimal Classification System – a user-friendly PowerPoint overview of the DDC provided by OCLC, the group that owns and manages the Dewey Decimal Classification system – Microsoft PowerPoint 2003 or higher (or a compatible program) required for viewing. 

Dewey decimal classification and relative index – why not read the current version of the whole thing?  (Four volumes, at Decatur Library reference department).  No, seriously – if you read this, you should really consider a career as a librarian!  🙂

{ 1 comment… read it below or add one }

RB November 16, 2012 at 1:43 PM

I’ve looked all over internet for explanation of how the digits to the right of the decimal are ordered. Everyone (including this page) stop short of this and then direct you to read the whole OCLC thing.

Are the tenths and hundredths similarly sub-divided?

For example, 823 = English Literature. What does 823.1 mean? 823.2? 823.3? etc. Is there a listing of the tenths?

Thanks – RB

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