Choosing a novel trim size: 5x8, 5.5x8.5, or 6x9?

Choosing a trim size for your novel isn’t about finding a single “correct” answer. In fiction, you’ll find three practical and universally supported options: 5 × 8, 5.5 × 8.5, and 6 × 9. Every major print-on-demand service—KDP, IngramSpark, B&N Press, Lulu—handles these sizes, and they all fit on standard bookstore shelves. Your choice isn’t about right versus wrong; it’s about the subtle signals you send to readers and the underlying economics of your book.

The Three Go-To Trim Sizes

5 × 8 — The Classic Pocket-Sized Paperback. This size evokes the feel of a traditional mass-market novel. It’s an excellent choice for shorter books, as it gives a 60,000-word manuscript satisfying heft without appearing too thin. You’ll often see this trim in romance, novellas, and shorter genre fiction.

5.5 × 8.5 — The Literary Digest. This trim has become shorthand for a “literary trade paperback.” It’s a popular choice for literary fiction, essay collections, and more subdued genre titles. Think of it as the middle ground: it offers more page area than a 5 × 8 book without assuming the bold, textbook-like presence of a 6 × 9.

6 × 9 — The Workhorse Trade Paperback. This is the most common size in self-publishing, a standard for commercial fiction, thrillers, epic fantasy, and most nonfiction. Its primary advantage is density: it fits more words on each page. For a long manuscript, this means fewer total pages, a slimmer spine, and a lower print cost.

How Trim Size Changes Your Book

Changing your trim size directly impacts your page count, setting off a chain reaction that affects your spine width, cover dimensions, printing costs, and even whether you can have text on the spine (which requires a minimum of 79 pages). As a rule of thumb, scaling up from 5 × 8 to 6 × 9 reduces your page count by about 20% to 25% for the same manuscript and interior layout.

This has several key implications you should calculate before deciding:

• Print Cost: Since KDP charges per page, the lower page count of a 6 × 9 book typically means a cheaper printing cost per copy, leaving more room for your royalty.
• Spine Presence: Fewer pages mean a thinner spine. A 320-page book at 5 × 8 will have a more substantial spine (with more room for title text) than the same text printed at 6 × 9.
• Cover Art: Each trim is a different rectangle (5×8 has a 1:1.6 ratio, 5.5×8.5 is about 1:1.55, and 6×9 is 1:1.5). Art designed for one size will be slightly cropped on another. Decide your trim size before finalizing your cover, and get the precise dimensions from the cover size calculator.

A Practical Starting Point

If you’re not sure what’s typical for your genre, here’s a sensible default: Use 6 × 9 for long books (90,000+ words or most nonfiction) and 5 × 8 or 5.5 × 8.5 for shorter fiction. The best next step? Go pull five successful books from your specific subgenre off the shelf—virtual or physical—and see what size they use. Aligning with your successful peers often matters more than any general guideline.

Sources

• Reedsy: Standard book sizes in publishing — genre conventions per trim
• Blurb: Standard book sizes & dimensions — trade paperback size ranges
• KDP: Print Options — supported trims and page ranges