What size of book, or trim size, are you planning for your work in progress? As everyone knows, size does matter. You want your book to fit in with the rest of those in its genre. Size impacts the number of pages of your book, the number of words per page, the margin size. Size also effects the cost of printing. Cost of printing changes the price of the book and the amount of royalties the author gets. So, again size matters.
We’re going to be talking in inches for this most. Inches are used in the US and millimeters pretty much everywhere else. And like most American’s I would have to use a conversation calculator to get the millimeters and thus just resort to using inches and hoping everyone else can convert. Sorry.
Typical paper back fiction novel sizes include 6 x 9, 5.5 x 8.5, 5.25 x 8, 5×8, and 4.25 x 6.87. Non fiction are 5.5 x 8.5, 6 x9, and 7 x10. Hard back novels are typically 6 x9 to 8.5 x 11. For children’s books you find 7.5 x 7.5, 7 x 10, 8 x 8, 8.5 x 8.5, 10 x10, and 10 x 8. Novellas are usually 5 x 8.
Here is an example about how size impacts costs:
100 pages = $4.45 on KDP and $3.58 on ingramspark
150 pages = $3.95 on KDP and $3.58 on ingramspark
200 pages = $3.35 on KDP and $3.58 on ingramspark
Why Ingramspark stays the same? I have no idea. Obviously cost of printing should not be the most important thing you consider when choosing the size of your book. First you need to check what sizes are offered by the printer/publisher you are using. Then look at your genre and see what some of the standard sizes are, then take into consideration the costs of printing.