E-books provided by 1. Publishers usually have font size setting options. In e-readers, you can usually adjust the font size by clicking or touching the screen. The specific operation method may be different for different readers. You can consult the reader's manual or look for related options in the settings menu.

2. In printed books, the font size is usually clearly marked in the preface or copyright page of the book. Generally, the description is "font size: 12". You can open the book to find this information, or look for relevant labels in the table of contents or back cover of the book.

If you borrow books from the library, you can ask the librarian, who usually knows how to check the font size of books.

4. In addition, there are some book reading applications or websites that provide online e-book reading services, and these platforms usually have font resizing options.

It should be noted that how to view the font size may be different for different book formats, publications and reading devices. Therefore, it is best to refer to the relevant instructions or consult relevant professionals to ensure the accuracy of the information.