Every nonfiction book in your library has a number address. Learn how the system works, then play four games to become a shelving pro!
A library can hold thousands of books. To keep them from turning into one giant pile, a librarian named Melvil Dewey came up with a clever idea in 1876: give every nonfiction book a number based on its topic. Books about the same subject get similar numbers, so they sit next to each other on the shelf. Find the number, and you find the book.
Every topic fits into one of ten main classes, numbered 000 to 900. Science is the 500s, art is the 700s, and so on.
Each group splits into smaller and smaller topics. 500 is science, 590 is animals, 599 is mammals. More digits means a more exact subject.
For even more detail, a decimal point and extra numbers are added — like 599.75 for big cats. That's the "decimal" in Dewey Decimal!
The number printed on a book's spine is its call number — its exact address on the shelf. It usually has two parts.
The top number is the Dewey number for the topic. The letters underneath are usually the first three letters of the author's last name. So 636.7 FET means "the dogs section, by an author whose name starts with FET." Books are shelved first by the number, then alphabetically by those letters.
Sometimes you'll see a short word above the number, like REF. That stands for Reference — books like dictionaries, encyclopedias, and atlases that you use inside the library but usually can't check out and take home. A reference book still has a normal Dewey number (a dictionary is 423); the REF just tells you it lives in the special reference area instead of on the regular shelves.
Here's a twist that trips up a lot of people: the Dewey Decimal System is for nonfiction (true information books). Most fiction — novels and chapter books that tell a made-up story — is shelved separately, in alphabetical order by the author's last name. So a Harry Potter book sits under "R" for Rowling, not under a Dewey number. Knowing whether a book is fiction or nonfiction is the very first step in finding it.
To make stories easier to find, libraries often split the fiction shelves into a few sections by reading level. You'll spot a short label on the spine that tells you which one a book belongs to:
Picture books for the youngest readers — short, with lots of pictures, and often read aloud. Some libraries label these E or PIC.
Chapter-book novels for readers who are ready for longer stories. Sometimes shown as just F, or J / J FIC for the younger "juvenile" shelves.
Novels written for teenage readers — roughly middle and high school age. The characters and storylines are usually more grown-up than the ones on the children's fiction shelves.
No matter which section it's in, fiction is still shelved A–Z by the author's last name — the label just tells you which set of shelves to start at.
Tap any group to see what kinds of books live there and a few real examples. These ten classes are the heart of the whole system.
A cart of returned books needs to go back on the shelves. Tap a book to pick it up, then tap the shelf where it belongs.
Books sit on the shelf in order from smallest number to largest — left to right. The tricky part is the decimals. Drag the cards into shelf order, then check your work.
A whole number like 636 means exactly the same as 636.0 — you can always imagine extra zeros hanging off the end (636.00, 636.000…). They don't change the value.
To compare two call numbers, line up the dots and check one digit at a time, left to right — like putting words in alphabetical order. The position of a digit matters more than how big it looks. Take 636.08 and 636.7:
The whole-number part (636) is a tie, so look at the first digit after the dot: that's 0 versus 7. Since 0 is smaller than 7, 636.08 comes first — even though the 8 on the end looks bigger than the 7! The librarian never even gets to that 8, because the first decimal digit already settled it.
Be a library detective! Read what each student is looking for, then pick the section where they should start hunting.
| Numbers | Main class | You'll find… |
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