* WorldCat ([worldcat.org](https://www.worldcat.org/)) is a database that contains records for books, articles, and other materials held by libraries around the world. The search results will include the book's Dewey Decimal number.
* Google Books ([books.google.com](https://books.google.com/)) allows users to search for books by title, author, or keyword. The search results will include the book's Dewey Decimal number.
* Amazon.com ([amazon.com](https://www.amazon.com/)) displays the Dewey Decimal number for books on their product pages.