Reference
Book trim sizes
Trim size is the finished dimensions of the printed page, and it is the first decision to make and the most expensive to change. It sets the page count, and the page count sets the gutter margin, the spine width and what the book costs to print.
This is the list of what is standard, what each size signals to a reader, and how to choose.
The common sizes, to scale
Numbers in a dropdown make these look like small variations on one another. They are not: the same manuscript at 4.25" × 7" and at 6" × 9" produces books that feel like different products.
Standard trim sizes by category
| Trim | Category | Typically used for |
|---|---|---|
| 4.25" × 7" | Mass market | Genre fiction, rack paperbacks |
| 4.37" × 7" | A-format | UK mass-market paperbacks |
| 5" × 8" | Small trade | Literary fiction, novellas, poetry |
| 5.06" × 7.81" | B-format | UK trade paperbacks |
| 5.25" × 8" | Small trade | Fiction, a slightly wider measure |
| 5.5" × 8.5" | Standard trade | The default for self-published novels |
| 5.83" × 8.27" | A5 | European standard, non-fiction and fiction |
| 6" × 9" | Large trade | Non-fiction, memoir, longer novels |
| 7" × 10" | Full size | Textbooks, illustrated non-fiction |
| 8.5" × 11" | Letter | Workbooks, manuals, worksheets |
How to choose
Start with your genre's shelf
Take three books off your own shelf that sit where you want yours to sit, and measure them. This is more reliable than any list, including the one above, because it encodes what readers in your genre already expect to hold.
Then check the page count
A novel that comes out under about 100 printed pages will look thin on a shelf and cannot carry text on its spine. One over 500 pages gets expensive to print and needs a wider gutter. If your manuscript lands at either extreme, the trim size is the lever.
Then check the cost
Work out the printing cost at your candidate trims and see what each leaves you at your intended price. For a long book this difference is not marginal — it can be the difference between a viable paperback and one that has to be priced above what the genre bears.
Alhora repaginates the whole book when you change trim, so the page count, spine width and printing cost all update together and you can compare candidates properly rather than estimating.
What the choice determines
- Page count
- A smaller page holds fewer words, so the same manuscript runs longer.
- Type size and measure
- A narrow page cannot carry large type without the line getting too short to justify cleanly.
- Gutter margin
- Set by page count, which is set by trim. Cross a band boundary and the interior needs re-setting.
- Spine width
- Page count × paper caliper. Which is why the cover comes last.
- Printing cost
- Fixed fee plus a per-page rate, so it tracks the page count.
- Shelf impression
- Readers have strong, unexamined expectations about what a book of a given kind should be.
Questions, answered
What is the most common book size?
6" × 9" is the most-used trim on Amazon KDP across both fiction and non-fiction, and it is the safe default if you have no other reason to choose. For novels specifically, 5.5" × 8.5" is the other standard and reads more like a trade paperback from a traditional publisher.
Does trim size affect printing cost?
Indirectly, and substantially. Print-on-demand charges a fixed fee plus a per-page rate, so the cost follows the page count — and a smaller page holds fewer words, so the same manuscript makes a longer, more expensive book. A 90,000-word novel is meaningfully cheaper to print at 6" × 9" than at 5" × 8".
Can I change the trim size after publishing?
You can, but it is a new interior file, a new spine width and therefore a new cover, and it repaginates the entire book. On KDP it is an update to the existing listing rather than a new edition, so reviews are kept. It is still an afternoon of work you avoid by choosing correctly at the start.
What size is a mass-market paperback?
Around 4.25" × 7", the rack-sized paperback sold in supermarkets and airports. Print-on-demand supports it, but be aware it is a format readers associate with traditionally published genre fiction — and it makes the thickest book from a given manuscript.
Should my ebook match my print trim size?
There is nothing to match. An ebook is reflowable: the reader chooses the type size and the text rewraps, so it has no trim size and no page count. The only place the two interact is the cover image, which should be readable as a thumbnail regardless.
What about hardcover?
Hardcover trims are usually the same page dimensions as the paperback — the case is built around the same book block. What changes is the cover: a case wrap adds board thickness and hinge grooves on top of the spine, so the cover sheet is larger than the paperback equivalent.
Try your book at three trim sizes
Alhora ships 23 trim presets plus fully custom sizes, and repaginates the whole book when you switch — so you can see the real page count at each before committing.
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