What Page Size (Trim Size) Should I Use for My KDP Book? Genre-by-Genre Guide
For most KDP books, the right trim size is 6″×9″ — it's the default for novels, nonfiction and self-help, and it looks professional while keeping page counts (and print costs) reasonable. Use 5.5″×8.5″ for romance, thrillers and other mass-market fiction where a more intimate, hold-in-one-hand feel matches genre expectations; 5″×8″ for a classic pocket-paperback look; and 8.5″×11″ (US Letter) for workbooks, journals, coloring books and anything readers write in. The rule that matters most: KDP will not let you change trim size after publishing, so choose before your first upload. Also watch the cost line — any trim wider than 6.12″ or taller than 9″ is classified as “large” and costs more per page ($0.017 vs $0.012 for black ink), lowering your royalty. Below is the full genre-by-genre guide plus the specs that make each size work.
The trim size cheat sheet by genre
| Genre / book type | Best KDP trim | Notes |
|---|---|---|
| Literary & general fiction | 6″ × 9″ | Authoritative, industry-standard |
| Romance | 5.5″ × 8.5″ or 5″ × 8″ | Intimate, mass-market feel |
| Thriller / mystery | 5.25″ × 8″ or 5.5″ × 8.5″ | Genre-standard digest sizes |
| Sci-fi / fantasy | 6″ × 9″ | Handles high word counts cleanly |
| Nonfiction / business | 6″ × 9″ | Roomy for headings and lists |
| Self-help | 5.5″ × 8.5″ or 6″ × 9″ | 6×9 reads more authoritative |
| Memoir | 5.5″ × 8.5″ | Personal, book-club feel |
| Poetry | 5″ × 8″ or 5.5″ × 8.5″ | Smaller trims suit short lines |
| Children's picture books | 8.5″ × 8.5″ or 8″ × 10″ | Large, image-friendly |
| Workbooks / journals | 8.5″ × 11″ | Buyers expect the writing space |
| Cookbooks / photo books | 8″ × 10″ or 8.5″ × 11″ | Showcases full-color images |
Why 6″×9″ is the default
6″×9″ is the most common trade paperback size on Amazon, so it signals “real book” to browsers, sits at the top of KDP's regular (non-large) cost tier, and fits more words per page than smaller trims — which lowers your page count and therefore your print cost. For a first-time novelist or nonfiction author unsure what to pick, 6″×9″ is the safe, professional default.
How trim size changes your print cost
Trim size affects cost two ways: directly (large trims cost more per page) and indirectly (a bigger page fits more words, so the same manuscript has fewer pages). On Amazon.com, black-ink regular-trim printing is $1.00 + $0.012/page; large trim jumps to $0.017/page.
| Trim | Class | Per-page (B&W) | ~250pp cost |
|---|---|---|---|
| 5″ × 8″ | Regular | $0.012 | $4.00 |
| 5.5″ × 8.5″ | Regular | $0.012 | $4.00 |
| 6″ × 9″ | Regular | $0.012 | $4.00 |
| 8.5″ × 11″ | Large | $0.017 | $5.25 |
Verify your exact figure on KDP's Printing Cost page — large-trim rates meaningfully reduce royalty per sale, so only go large when your content (workbooks, photo-heavy books) truly needs it.
The specs that come with your trim choice
- Margins: outside ≥0.25″; gutter scales with page count (0.375″ up to 150pp, 0.5″ for 151–300pp, 0.625″ for 301–500pp).
- Spine text: only on books with 79+ pages — thinner books get a blank spine regardless of trim.
- Bleed: if art runs to the edge, extend it 0.125″ past trim and size the PDF 0.25″ taller and 0.125″ wider.
- Match the category: search your genre's top 10 on Amazon and note their trims — fitting in usually beats standing out.
Can you use a custom (non-standard) trim size?
Yes. Beyond its 16 standard paperback sizes, KDP lets you set a custom trim anywhere from 4″–8.5″ wide and 6″–11.69″ tall. But there are good reasons most authors stick to standard sizes:
- Distribution limits: some custom sizes aren't eligible for Expanded Distribution or hardcover, narrowing where your book can sell.
- Reader expectations: an unusual size can look 'off' next to genre norms on a shelf or in a photo.
- Cover templates: standard sizes have ready-made templates; custom sizes mean calculating everything yourself.
- No cost advantage: custom sizes follow the same regular/large cost tiers, so there's rarely a pricing upside.
Custom trims make sense for special formats — square children's books, unusual art books, branded workbooks — but for a standard novel or nonfiction title, a stock size is almost always the smarter choice.
What about hardcover and ebook trim sizes?
Trim size works differently across formats:
- Hardcover: KDP offers five sizes (5.5″×8.5″, 6″×9″, 6.14″×9.21″, 7″×10″, 8.25″×11″). If you plan a hardcover edition, pick a paperback trim that also exists in hardcover so you don't have to reformat.
- Ebook: there is no trim size — EPUB and Kindle files are reflowable, adapting to each reader's screen. Trim only matters for print.
- Consistency: if you're publishing paperback, hardcover and ebook, format the print editions to matching trims for a coherent series look.
How to choose when you're genuinely unsure
When in doubt, let the market decide for you:
- Search your exact genre's top 10 bestsellers on Amazon.
- Open each book's product details and note the listed dimensions — that's the trim.
- Pick the size that appears most often. Matching category norms helps your book 'fit in' with proven sellers.
- Default to 6″×9″ only if the results are mixed or unclear.
The mistake that can't be undone
Because trim size is locked after publishing, picking wrong means republishing as a brand-new listing — losing your reviews, ranking and sales history. This is the most expensive DIY mistake in self-publishing, and it's entirely preventable.