The short answer
8.5 × 11 inches (216 × 279 mm) is the standard coloring book size in the US, and the one most self-published coloring books use. It matches US Letter paper, so a buyer who wants to photocopy a page can, and it gives an adult colorist enough room for detail without the book becoming unwieldy.
In Europe the equivalent expectation is A4 — 8.27 × 11.69 inches (210 × 297 mm). It is almost the same size and it is not interchangeable, for a reason covered below that costs you money rather than millimetres.
The standard sizes
| Size (in) | mm | Who uses it |
|---|---|---|
| 8.5 × 11 | 216 × 279 | The default. US Letter. Adult and children’s alike. |
| 8.27 × 11.69 | 210 × 297 (A4) | European expectation. Prints cleanly on home A4 paper. |
| 8 × 10 | 203 × 254 | Slightly smaller, cheaper per unit, still roomy. |
| 8.25 × 8.25 8.5 × 8.5 | 210 × 210 216 × 216 | The two squares KDP offers. Distinctive on a shelf, awkward to photocopy. |
| 6 × 9 | 152 × 229 | Travel and pocket books. Too small for detailed adult work. |
What KDP actually offers
If you are printing through Amazon KDP, the trim size dropdown groups sizes into three sections, and which section your size falls into matters more than the dimensions do.
- Most Popular Standard: 5 × 8, 5.25 × 8, 5.5 × 8.5, 6 × 9
- More Standard: 5.06 × 7.81, 6.14 × 9.21, 6.69 × 9.61, 7 × 10, 7.44 × 9.69, 7.5 × 9.25, 8 × 10, 8.5 × 11
- Non-Standard: 8.27 × 11.69 (A4), 8.25 × 6, 8.25 × 8.25 and 8.5 × 8.5 (the two squares), plus Custom
Non-Standard trims are printable and orderable, but they are not eligible for Expanded Distribution — the channel that puts your book in front of bookshops, libraries and non-Amazon retailers. Choosing A4 or square is therefore a distribution decision wearing the costume of a paper-size decision, and it is the single most common thing people get wrong here.
8.5 × 11 is the only large format that is both the market standard and Expanded-Distribution eligible. That is why it is the default recommendation and not merely a convention.
A4 vs Letter
They differ by about 6 mm in width and 18 mm in height — close enough that artwork designed for one can usually be adapted to the other, and different enough that you should not simply scale and hope.
The honest split:
- Selling mainly to the US, or want bookshop distribution: 8.5 × 11.
- Selling mainly in Europe, or selling a printable PDF people run off at home: A4, because a Letter-sized page sent to a European home printer either gets cropped or gets shrunk by “Fit to Page”.
- Doing both: produce both. The relaid pages are a fraction of the work of drawing them, and it removes the question entirely — which is why our own coloring packs ship in A4 and Letter rather than picking a side.
Single-sided vs double-sided
This is a bigger decision than trim size and gets far less attention.
Alcohol markers and most felt tips bleed through standard book paper. If your pages are printed on both sides, a colorist using markers destroys the drawing on the reverse — which is why adult coloring books are so often printed single-sided, with the back of each illustration left blank.
The consequence is arithmetic: a 50-illustration single-sided book is a 100-page book. That roughly doubles your print cost per unit and moves you up KDP’s page-count bands. It is the right call for an adult marker-oriented book and usually the wrong one for a children’s crayon book, where bleed-through is not a real risk.
A middle path some publishers take is double-sided pages with a perforated or clearly marked cut line, so a colorist can remove the sheet before working on it. It is a design decision, not a size one, but it changes the page count you need to plan for.
Bleed and margins
Two numbers do most of the work here, and they are the same ones that apply to any KDP interior:
- Bleed is 0.125 inches per side. A page designed to bleed is your trim size plus 0.25 inches total in each dimension — so an 8.5 × 11 book with bleed is an 8.75 × 11.25 page. That outer margin is cut off and thrown away.
- Keep anything that matters 0.375 inches inside the trim. This is the safety area, and a guillotine drifts.
Coloring books have one margin consideration most books do not: the gutter, the inner edge swallowed by the binding. People press hard on a coloring page and try to flatten the book, so line art that runs into the gutter is both hard to reach and prone to cracking the spine. Give the inner edge more room than you think you need, and avoid running a drawing across the spine at all unless the book is designed to lie flat.
Many coloring books simply do not bleed — the illustration sits inside a white border on every page. That is a legitimate choice, it is more forgiving to print, and it makes the page photocopiable.
How to choose
Working backwards from what you want:
- Widest reach and fewest surprises: 8.5 × 11, double-sided for children, single-sided for adults.
- European market or a printable download: A4, and accept that Expanded Distribution is off the table if you print through KDP.
- Lower unit cost: 8 × 10 — still a Standard trim, noticeably cheaper, and few buyers will notice the difference.
- Something that stands out on a shelf: 8.25 × 8.25 or 8.5 × 8.5 square, knowing both are Non-Standard and neither photocopies onto a normal sheet.
Whatever you pick, decide before the artwork is drawn. A coloring page composed for a portrait trim does not become a square by scaling, and redrawing a book to fit a different size costs far more than choosing correctly at the start. The same is true of picture books — see our picture book trim size guide for that decision, and how to design a coloring book for everything that comes after the size.