What Is the Dewey Decimal System?

By the Public-Libraries.com Editorial Team · Updated October 5, 2026

What the Dewey Decimal system is

The Dewey Decimal Classification is a way of putting every non-fiction book on a shelf by what it’s about rather than by author or title. Each subject is assigned a number, similar subjects sit next to each other, and the numbers run in order along the shelves — so once you know a book’s number, you can walk straight to it (and browse everything nearby on the same topic). As of the most recent published figure (2009), it was used in roughly 200,000 libraries across 135+ countries and has been translated into more than a dozen languages.

It is a proprietary system: all rights are owned by OCLC (the Online Computer Library Center), which maintains the live, continuously updated edition (“WebDewey”) that cataloguers use. Fiction, by the way, usually escapes Dewey entirely — most libraries shelve novels alphabetically by the author’s last name instead.

How the Dewey Decimal system works

Dewey divides all of human knowledge into 10 main classes. Each class splits into 10 divisions, and each division into 10 sections — so three digits already give you 1,000 basic categories. When a topic needs to be more specific, a decimal point is added and the number keeps growing. Nothing ever “runs out” of numbers, because you can always add another decimal place.

You can watch a subject get narrower one digit at a time: 500 is science, 510 is mathematics, 516 is geometry, 516.3 is analytic geometry, and 516.375 pins down one very specific corner of it. The further right you read, the more specialized the book.

The 10 Dewey Decimal classes (000–900)

A Dewey Decimal chart: all 100 divisions

Each of the 10 classes splits into 10 divisions — the 100 two-digit numbers below, what OCLC calls the “Second Summary.” This is the quick chart most people are really after: find your class, then scan its divisions. (The official summaries stop at three digits; beyond that, the full schedule keeps adding decimals to get more specific.)

How to read a call number

A full Dewey call number has two parts. The top line is the subject number (from the classes above). The bottom line is usually a “Cutter number” — a short letter-and-number code standing in for the author’s last name, so books on the same topic line up alphabetically by author. Read it top to bottom: first find the subject number on the shelf, then move alphabetically to the author.

How to look up a book’s Dewey number

You don’t need special software to find a book’s Dewey number. Three free ways, easiest first:

1. Search a library catalog. Look the title up in any library’s online catalog (OPAC), or on WorldCat.org, and read the call number on the record — that is the assigned Dewey number.

2. Check the copyright page. Many books print a Cataloging-in-Publication (CIP) block on the copyright/verso page, prepared by the Library of Congress before publication. Its classification line shows the Dewey number, written like DDC 813/.6—dc23 (the dc23 simply means it was assigned using Dewey edition 23). Not every book carries a DDC number there, so this won’t always work.

3. The official source. Cataloguers themselves assign numbers with OCLC’s WebDewey, the subscription database that is the live, continuously updated edition of the full classification. It’s overkill for a single lookup, but it’s where the numbers officially come from.

Famous Dewey numbers you may have wondered about

A handful of numbers are oddly memorable because people search for them by heart:

Who invented it? Melvil Dewey’s complicated legacy

The system was created by Melvil Dewey (1851–1931) while he worked at Amherst College, and first published in 1876 as a slim 44-page pamphlet. It has since gone through 23 major editions. Dewey was a genuine pioneer of American librarianship — but his personal record is troubling, and it’s worth being honest about it.

Dewey wrote the exclusionary membership rules for the Lake Placid Club he founded, barring Jewish and Black members; he faced a 1905 rebuke from the New York State Board of Regents and resigned his state library post; and he was documented making unwanted advances toward women, including several librarians on a 1905 professional trip. In 2019, the American Library Association voted to strip his name from its top honor — the “Melvil Dewey Medal,” awarded since 1953, was renamed the ALA Medal of Excellence — citing his “well-documented history of racism, anti-Semitism, and sexual harassment.” The classification he built lives on; the veneration of the man does not.

What about fiction and biographies?

Here’s the catch that surprises many readers: Dewey only classifies non-fiction. Novels and short-story collections almost never get a Dewey number. Instead, most U.S. public libraries shelve fiction alphabetically by the author’s last name in a separate section — the spine label usually just reads FIC or F plus the first letters of the surname (for example, FIC KING for a Stephen King novel). Many libraries break fiction out further into genre areas such as Mystery, Science Fiction, Romance or Graphic Novels.

Biographies are a gray area: some libraries file them in Dewey’s 920s (biography) or use 92 / B, while others keep a dedicated Biography section arranged by the subject’s last name. Children’s picture books are likewise usually grouped in their own E (Easy) or picture-book area rather than by Dewey number. When in doubt, the library’s online catalog always lists the exact call number and location for a given title.

Is the Dewey Decimal system still used?

Yes — in the U.S. it remains the standard in public libraries and most school libraries. Large academic and research libraries generally use a different scheme, the Library of Congress Classification, which handles huge specialized collections better.

There is a real, growing exception, though. Since around 2007–08 — when Arizona’s Maricopa County Library District famously switched — some public libraries have dropped Dewey (often just in the children’s or teen sections) in favor of word-based, bookstore-style categories such as the BISAC scheme used by Amazon and Barnes & Noble. The goal is browsability: grouping books under plain labels like “Cooking” or “Mystery” instead of numbers. Critics of Dewey also point to its built-in biases (for instance, most of the world’s literature is squeezed into the 890s while European literature sprawls across 810–889). So Dewey is far from dead — but it’s no longer the only option on the shelf.

Dewey Decimal vs. Library of Congress Classification

Whichever system your library uses, the online catalog will always tell you the exact call number — and if you get stuck, a librarian can point you to the right shelf in seconds. To find the library nearest you, browse our directory of U.S. public libraries by state and city.

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