Measure the height and total width (front + spine + back) of the book you wish to protect, then select the appropriate size of book protector from the list of available sizes.
For paperbacks select a book protector with a height that is the same as or slightly larger (up to 4mm) than the measured height of your book.
For hardbacks select a book protector with a height that is at least 2mm and up to 6mm larger than the measured height of your book.
The total width of the book protector must be no less than the measured total width of your book.