It really varies. Novels can range from a few megabytes to tens of megabytes, depending on factors like length, formatting, and included images.
The average file size of a novel is quite unpredictable. It could be as small as 500 kilobytes for a very short and simply formatted one, or it could go up to 20 megabytes or more for a lengthy, elaborately formatted novel with lots of extras. Generally, it's somewhere in between.
The average file size of a novel is hard to pin down exactly. It depends on a lot of things. Longer novels, complex formatting, and maybe even embedded illustrations can make the file size larger. Shorter novels with simple formatting will be smaller. On average, though, it could be anywhere from 1 to 10 megabytes.