6 by 9 inches is the answer you will get everywhere, and it is a reasonable default. But it is worth knowing what that claim actually rests on, because no publisher catalogue, library dataset or trade body publishes figures on novel trim sizes. Nobody has counted.
What exists is one first-party statement about US books in general, plus a set of platform defaults that everyone has reasoned backwards from.
What Is Actually Sourced
Amazon's statement, which is about books rather than novels. KDP's Print Options page says: "The most common trim size for books in the U.S. is 6" x 9" (152.4 x 228.6 mm) and is a regular trim size. When setting up your book, this is the default in the "Print Options" section of the Content tab."
Note the scope. That is a claim about US books, from the platform that prints a very large share of them, and it is the strongest evidence available. It is not a claim about novels.
Platform defaults and naming. 6 by 9 is KDP's setup default. Lulu names it "US Trade", which is the trade paperback category name. Both are meaningful signals about market expectation.
A statement about finish, not size. KDP says matte finish "is typical for novels and other fiction", which is the only place a major platform says anything specific about novels at all, and it is about lamination.
A statement about binding, not size. IngramSpark says "The perfect bound trade paperback is the most commonly printed book in the indie publishing arena". Again, that is binding, not dimensions.
Put together: 6 by 9 is defensibly the most common size for US books, and it is the default everywhere. Whether it is the most common size for novels specifically is a question nobody has published an answer to.
Why the Answer Might Differ for Novels
There is a real reason to think fiction skews smaller, and it is arithmetic rather than taste.
A larger page holds more words, so the same manuscript produces fewer pages. A 70,000 word novel at 6 by 9 makes a thin book. The same novel at 5 by 8 or 5.5 by 8.5 makes a noticeably thicker one, with a spine wide enough to carry a title, since spine width is page count multiplied by paper thickness and KDP prints no spine text below 80 pages at all.
Non-fiction, textbooks and illustrated books, which make up much of the "US books" population that 6 by 9 leads, have no such pressure. They tend to be longer and to need the wider measure for tables, figures and quoted material.
So the honest position is: 6 by 9 leads across all US books, fiction plausibly skews smaller, and nobody has measured it. Treat any article that gives you a percentage as having invented it.
The Sizes That Actually Compete
Four sizes account for nearly all English language novels:
| Size | Millimetres | Character |
|---|---|---|
| 5 x 8 | 127 x 203.2 | Compact. Literary fiction, novellas, poetry |
| 5.25 x 8 | 133.4 x 203.2 | Paperback only, no hardcover anywhere |
| 5.5 x 8.5 | 139.7 x 215.9 | Smallest size with no availability gaps |
| 6 x 9 | 152.4 x 228.6 | The default. Full availability everywhere |
In the UK and Europe the equivalents are metric and the vocabulary differs. The industry metadata standard ONIX defines the British categories by measurement: A-format paperback is "normally 178 x 111 mm approx" and B-format is "normally 198 x 129 mm approx". Neither is offered as a named size by KDP, IngramSpark or Lulu, so a UK self publisher reaches B-format only through IngramSpark's custom trim.
For mass market, ONIX defines the North American rack paperback as "typically from 6¾ up to 7⅛ x 4¼ inches", a category defined "partly by page size and partly by target market and terms of trade". That is the drugstore paperback, and it is not available through print on demand at all.
What to Actually Do
Do not choose by popularity. Choose by page count, because that is what determines whether the finished book feels right and whether the spine works.
Roughly: under 60,000 words, look at 5 by 8. Between 60,000 and 100,000, 5.5 by 8.5 or 6 by 9. Over 120,000, 6 by 9, both because the page count stays manageable and because the platform ceilings matter. Those are guidelines rather than rules, and the deciding factor is what the object feels like in the hand.
The one thing worth checking before you commit is availability, since the smaller sizes close off options. 5.25 by 8 has no hardcover at either platform. 5 by 8 has no KDP hardcover. Full detail in book trim sizes explained.
What Deckle Does
Deckle defaults to 6 by 9, matching KDP's default, and offers six sizes in total: 5 by 8, 5.5 by 8.5, 6 by 9, 6.14 by 9.21, BoD 135 by 215 mm and A5 148 by 210 mm.
The useful feature when weighing this decision is the estimated page count, shown before you export. Because trim size drives page count and page count drives spine width, gutter requirement and printing cost, you can compare sizes on the number that actually matters rather than on which one sounds standard.
Note that changing trim size reflows the entire book, so this is a decision to make early rather than adjust late.
Common Mistakes
- Treating "6 by 9 is most common" as a fact about novels. The sourced claim is about US books generally.
- Believing a percentage. No dataset on novel trim sizes exists to derive one from.
- Choosing by popularity rather than page count. A short novel at 6 by 9 looks thin.
- Ignoring the spine. Under 80 pages KDP prints no spine text at all.
- Assuming UK sizes are available. A-format and B-format are not listed at any major platform.
- Changing size late. It reflows everything downstream.
FAQ
Q: So what size should I use? A: 6 by 9 for most novels over 80,000 words, 5.5 by 8.5 or 5 by 8 below that. Decide on page count, not popularity.
Q: Is 6 by 9 really the most common? A: For US books generally, Amazon says so and it is the default. For novels specifically, no one has published data.
Q: What is a mass market paperback? A: The rack sized paperback, defined by ONIX as roughly 6¾ to 7⅛ by 4¼ inches. It is not available through print on demand.
Q: What do UK publishers use? A: A-format at about 178 by 111 mm and B-format at about 198 by 129 mm, neither of which is a listed print on demand size.
Q: Does trim size affect what I earn? A: Indirectly. It changes page count, which changes printing cost, which changes royalty at a given price.