THE FIRST DIGIT
Ten main classes
Dewey divides all knowledge into ten main classes, from 000 for computer science and general works to 900 for history and geography.
Try a bookThe number on the spine is a map reference.
Libraries in more than 135 countries use the Dewey Decimal Classification, first published in 1876. Learn to read its three digits and the decimal point, and any library starts to make sense.
- Ten main classes
- Each split by ten
- Decimals go deeper
- Read the number, find the shelf
THE SHORT ANSWER
Three digits,
then a dot.
Dewey sorts books by subject, not by author or title.
The number gets longer as the subject gets narrower.
THE NEXT DIGITS
Tens within tens
Each class splits into ten divisions and each division into ten sections. So 600 is technology, 630 agriculture, 636 animal husbandry.
See the ladder
AFTER THE DOT
Narrower and narrower
Digits after the decimal point go deeper still: 636.7 is dogs and 636.8 is cats. Longer numbers mean more specific subjects.
Find a book
FOUR STEPS IN ANY LIBRARY
From catalogue
to shelf.
The same routine works in a school, public or university library that uses Dewey. It only takes reading the number in order.
Look up the number
Search the library catalogue and note the full class number, decimals included.
Find the hundred
Walk to the right main class first: 600s for technology, 900s for history and geography.
Follow the digits
Read left to right. 636 comes before 641, and 636.7 before 636.8.
Browse the neighbours
Books on related subjects share the first digits, so the shelf around your book is worth a look.
TWO NUMBERS WORTH KNOWING
One system,
a world of shelves.
How far Dewey reached,
and how many new numbers it still needs.
135+ countries
Countries whose libraries use Dewey
OCLC's introduction to the system says libraries in more than 135 countries use Dewey, and that Dewey numbers appear in the national bibliographies of more than 60 countries.
REACH · OCLC
48,893
Dewey numbers added in one year
The Library of Congress contributed 48,893 standard Dewey numbers in original cataloguing records in its 2013 financial year. In the 1970s and 1980s it added close to 100,000 a year.
NEW NUMBERS · LIBRARY OF CONGRESS
Dewey is revised continuously. The Library of Congress FAQ names Edition 23 as the current edition, and OCLC now publishes Dewey online as WebDewey.
A QUICK SHELF CHECK
Where would
this book live?
Pick a kind of book to see its Dewey number. The bar shows how far along the 000 to 999 run of shelves it sits.
Numbers from OCLC's published Dewey Decimal Classification summaries. Your library may add letters or local labels to them.
DEWEY OR LC?
Numbers here,
letters there.
The main alternative is Library of Congress Classification. It was developed at the turn of the 20th century for the Library of Congress and has 21 main classes, each with a letter: L for education, J for political science, Q for science.
Dewey keeps to numbers and a strict ladder: a number one digit shorter is broader, and one digit longer is narrower. A subject can live in more than one place: OCLC's example is clothing, at 155.95 for its psychology, 391 for customs and 746.92 for fashion design.
In conversation
Questions people ask
Who invented the Dewey Decimal Classification?
OCLC says it was conceived by Melvil Dewey in 1873 and first published in 1876. It is now published by OCLC, with an editorial office at the Library of Congress.
What are the ten Dewey main classes?
000 computer science, information and general works; 100 philosophy and psychology; 200 religion; 300 social sciences; 400 language; 500 science; 600 technology; 700 arts and recreation; 800 literature; 900 history and geography.
What does the decimal point do?
It comes after the third digit. OCLC explains that division by ten then continues after the point to whatever level of detail is needed, so 636.7 (dogs) is narrower than 636 (animal husbandry).
Why can one subject have several numbers?
Dewey sorts by discipline. OCLC's example is clothing, which sits at 155.95 for its psychology, 391 for customs and 746.92 for fashion design.
How is Library of Congress Classification different?
The Library of Congress says LCC uses 21 subject categories marked by letters and numbers, while Dewey is strictly numeric apart from a few options, with ten classes each split into ten divisions and ten sections.
Sources
Each figure on this page comes from the sources below.