Guides › Trim sizes
Choosing a trim size
By Lukas · updated
The trim size is the size of the finished page, and it is the first decision in formatting a book because the margins, the page count and the cover all follow from it. KDP and BoD each have their own list, and the size you pick changes the page count more than most people expect.
What most books use
There is no rule, only habits, and the habits come from what readers have on their shelves. For a novel, look at a few in your genre from the last couple of years and measure them. You will mostly find these:
| Book | Usual trim |
|---|---|
| Novels | 5 × 8, 5.25 × 8 or 5.5 × 8.5 in; 6 × 9 in for long ones |
| Non-fiction, memoir | 5.5 × 8.5 or 6 × 9 in |
| Poetry | 5 × 8 or 5.5 × 8.5 in, wide enough for the longest line |
| Workbooks, journals | 7 × 10 or 8.5 × 11 in |
| Picture books | 8.5 × 8.5 or 8 × 10 in |
6 × 9 in is where many self-publishing guides start, and it suits most non-fiction. A smaller trim feels more like a novel from a bookshop and is easier to hold, but it makes the book thicker.
KDP’s sizes
KDP lists 5 × 8, 5.25 × 8, 5.5 × 8.5, 6 × 9, 6.14 × 9.21, 7 × 10, 8 × 10, 8.5 × 8.5, 8.27 × 11.69 (A4) and 8.5 × 11 in. A custom size is allowed from 4 to 8.5 in wide and 6 to 11.69 in tall. Anything wider than 6.12 in or taller than 9 in counts as a large trim and costs more to print. The KDP paperback guide has the margins and the rest.
BoD’s sizes
Books on Demand, the main print-on-demand service in Germany, offers ten sizes in centimetres: 12 × 19, 13.5 × 21.5, A5 (14.8 × 21), 15.5 × 22, 17 × 22, 17 × 17, 21 × 15 (landscape), 19 × 27, 21 × 21 and A4 (21 × 29.7). 12 × 19 cm is the German mass-market paperback (Taschenbuch), 13.5 × 21.5 cm the larger trade paperback many publishers now use. Only A4 is on both lists, though most of BoD’s sizes can be set as a KDP custom size. A book printed with both still usually needs two files, because the margins and bleed differ.
What the size does to the page count
A smaller page holds fewer words, so the same text makes more pages. I set a novel of 80,000 words in 25 chapters at 11 pt with Kernsetzer at each size:
| Trim | Pages | At 12 pt |
|---|---|---|
| 5 × 8 in | about 294 | about 338 |
| 5.25 × 8 in | about 286 | about 322 |
| 5.5 × 8.5 in | about 262 | about 302 |
| 6 × 9 in | about 244 | about 270 |
Fifty extra pages cost about 60 cents more per copy at KDP’s US price for black ink, they widen the spine by an eighth of an inch, and past 300 pages KDP wants a wider gutter. None of that makes a small trim wrong, but it is worth knowing before you choose. The page count calculator works it out for your own book.
Changing the size later
Decide the size before you typeset, not after. A new size reflows every page and changes the page count, the gutter and the cover. On KDP, the trim size can’t be changed once the book is published; you publish it as a new edition.
In Kernsetzer the trim size is a menu: pick another and the whole book is set again, margins and all, so you can try a few sizes and look at the page count before you decide. Sign up for the beta.
Sources: KDP’s help page on trim size, bleed and margins, checked on 28 October 2026, and BoD’s author brochure, checked on 21 October 2026. Both change their lists from time to time, so check them before you order a proof. The page counts are Kernsetzer’s, with the Classic theme; other fonts and margins give other numbers.