Trim sizes and interior formatting basics for print books

A print book’s interior is made of decisions readers never notice when they’re right: the page size, the margins, the typeface, the space between lines. When any of them is wrong, readers notice immediately, and the printer may reject the file before a reader ever sees it.

This guide covers the basics for self-published paperbacks, using Amazon KDP’s requirements as the reference point. Other printers have similar rules; check their specifications before you export.

Choose the trim size first

Trim size is the finished page size. Choose it before you format anything, because everything else depends on it: page count, printing cost, spine width, and the cover.

Common choices for US paperbacks:

• Fiction: 5 x 8, 5.25 x 8, 5.5 x 8.5, or 6 x 9 inches
• Nonfiction: 6 x 9 inches, which KDP notes is the most common paperback trim in the US
• Workbooks and manuals: 8.5 x 11 inches, with room to write
• Picture books: square or landscape formats, such as 8.5 x 8.5 or 8 x 10 inches

The simplest way to decide is to check comparable books. Amazon product pages list dimensions in the product details, and a few minutes with a ruler in a bookstore tells you what readers in your genre are used to holding.

Two practical effects of trim size:

• Page count. A smaller page holds fewer words, so the same manuscript makes a thicker book with a higher printing cost.
• Cost tier. KDP treats any trim wider than 6.12 inches or taller than 9 inches as large trim, which costs more per page to print.

Margins: KDP’s minimums

KDP requires an inside margin, the gutter next to the binding, that grows with page count, because thicker books curve more at the spine:

The top, bottom, and outside margins must be at least 0.25 inch without bleed, and at least 0.375 inch with bleed.

These are minimums, not recommendations. Text that runs close to the edges looks cramped and is uncomfortable to hold. Professionally designed books typically use noticeably wider margins, especially on the outside edge, where thumbs rest.

Bleed, if anything touches the edge

Bleed is needed only when images or background colors run to the edge of the page. On KDP, bleed adds 0.125 inch to the top, bottom, and outside edge, so a 6 x 9 inch book with bleed uses a page size of 6.125 x 9.25 inches. The extra is trimmed off after printing.

If your book is text only, don’t use bleed. If even one page needs it, the whole interior has to be set up with bleed. Either way, keep text and important details inside the margins, because trimming can vary slightly from copy to copy.

Type and spacing

• Typeface: a serif designed for books, set at 10 to 12 points for body text. Test-print a page, because sizes look different on paper than on screen.
• Leading: line spacing of about 1.2 to 1.5 times the type size, such as 11-point type on 14-point leading.
• Alignment: justified text with hyphenation turned on, which avoids large gaps between words.
• Paragraphs: in fiction, indent the first line of each paragraph and don’t add space between paragraphs. Don’t indent the first paragraph of a chapter or the first paragraph after a scene break.
• Scene breaks: a centered symbol or a blank line, used the same way every time. A blank line that falls at the bottom of a page can disappear, so a symbol is safer.
• Widows and orphans: avoid single lines stranded at the top or bottom of a page.

Page furniture

• Page numbers on every page except blank pages and, usually, chapter openings
• Running heads at the top of each page, often the author’s name on left-hand pages and the title on right-hand pages, left off chapter openings and blank pages
• Chapter openings that start lower on the page, sometimes with a drop cap or small capitals for the first words
• Right-hand starts: many books start each chapter on a right-hand, odd-numbered page. It’s common in nonfiction and optional in fiction, but it adds blank pages and therefore cost.

Front and back matter

A common order for front matter is half title, title page, copyright page, dedication, epigraph, and table of contents. Fiction paperbacks often leave out the table of contents; nonfiction should keep it. Back matter can include acknowledgments, an author’s note, an about-the-author page, a list of other books, and an invitation to your newsletter.

Paper and spine

KDP offers several paper options for black-ink interiors, including white and cream; color interiors print on white. The paper and the page count set the spine width, which your cover designer needs, and KDP only allows text on the spine once a book passes a minimum page count, around 80 pages at the time of writing. KDP’s cover calculator and templates give exact dimensions for your page count and paper.

Because the spine depends on the final page count, finish the interior before the full cover is built. Adding even a few pages after the cover is done means resizing the spine.

Export and check

• Export a PDF at the trim size, with bleed only if needed
• Embed all fonts
• Use images at 300 DPI at the size they’ll print
• Upload to KDP and page through the previewer, which flags margin and bleed problems
• Order a printed proof and read it on paper before you approve the book

A printed proof catches things no screen will: type that’s too small, margins that feel tight in the hand, images that print darker than expected, and a gutter that swallows words in a thick book.

Common reasons files get flagged

• Text or images that cross into the minimum margins, often a page number or a running head placed too close to the edge
• Bleed set up incorrectly, with art that should reach the edge stopping short of the extra 0.125 inch
• Low-resolution images that look fine on screen and blurry in print
• Fonts not embedded in the PDF
• A page size that doesn’t match the trim size chosen in the book’s setup
• A cover built for a different page count than the final interior

Each of these is easier to fix before upload than after a rejection, so check them against your final PDF.

Ebooks are formatted differently

Everything above applies to print. An ebook is reflowable: readers choose their own font and size, so there are no fixed pages, page numbers, or running heads, and margins are set by the reading device. Format the ebook from the same manuscript, but as a separate file built for reflow.

Interior formatting checklist

• Trim size chosen to match comparable books
• Margins at or above KDP’s minimums for your page count
• Bleed set up only if art or color reaches the edge
• Body type, leading, and paragraph style consistent throughout
• Page numbers and running heads correct, and absent where they should be
• Front and back matter complete
• Fonts embedded and images at print resolution
• A printed proof checked

Picture books and other illustrated books have extra considerations for spreads and the gutter; see writing a picture book.

On the Pro plan, AIBookWriter’s Format & export step produces a print-ready PDF with trim sizes and themes, runs preflight checks, and calculates the spine width for paperback covers. If you’re still estimating length, the free Word Counter gives word, page, and per-chapter counts in your browser.