Trim size is the final width and height of your printed book after it is cut during production. It affects how your book looks, how it feels to hold, how many pages it has, and how much it costs to print.

For fiction, the most common trim sizes are 5"×8" and 5.5"×8.5". These are standard novel sizes that readers expect. They are comfortable to hold and look consistent with traditionally published books. Smaller mass market sizes (around 4.25"×6.87") are typically not available to self-publishers using print-on-demand.

For nonfiction, 6"×9" is the industry standard. The larger page size allows for longer paragraphs, better spacing, and room for charts, tables, or images. Most business books, memoirs, and self-help titles use this format.

For children’s and illustrated books, larger formats are common. Sizes like 8.5"×8.5" (square) or 8.5"×11" give artwork space and improve visual presentation.

Trim size directly impacts page count and printing cost. A smaller trim size results in more pages, while a larger trim size reduces page count. Fewer pages usually lower printing costs, but can make the book feel thin. More pages increase spine width and perceived value, but also increase production cost.

Both KDP and IngramSpark support standard and custom trim sizes. KDP offers many standard sizes, but custom sizes may not qualify for expanded distribution. IngramSpark allows broader distribution, though some retailers prefer standard dimensions.

The best approach is to match your genre. Look at top-selling books in your category and note their trim sizes. Readers are used to certain dimensions, and a book that feels off — too large, too small, or awkward — can create a negative impression even if the content is strong.

Sources:

• KDP Help: Supported Trim Sizes
• IngramSpark Trim Size Guide
• BookDesignTemplates.com Trim Size Recommendations