Short answer: the standard UK book sizes are A-format 111 × 178 mm, B-format 129 × 198 mm and Demy 138 × 216 mm for paperbacks, and Demy, Royal 156 × 234 mm or Crown Quarto 189 × 246 mm for hardbacks and larger non-fiction. A5 is 148 × 210 mm. If you publish on Amazon KDP you choose in inches, and three KDP sizes are the UK formats to within half a millimetre. The table shows which.
UK book sizes in mm, cm and inches
| UK name | Size (width × height) | Inches | Nearest Amazon KDP size | Typical use |
|---|---|---|---|---|
| A6 | 105 × 148 mm 10.5 × 14.8 cm | 4.13 × 5.83 | None | Pocket books, booklets |
| A-format | 111 × 178 mm 11.1 × 17.8 cm | 4.37 × 7.01 | None (smallest KDP size is 5 × 8 in) | Mass-market paperback |
| B-format | 129 × 198 mm 12.9 × 19.8 cm | 5.08 × 7.80 | 5.06 × 7.81 in (128.5 × 198.4 mm) | Paperback novels; Penguin Classics |
| C-format | 135 × 216 mm 13.5 × 21.6 cm | 5.31 × 8.50 | 5.5 × 8.5 in (4.7 mm wider) | Larger trade paperbacks |
| Demy | 138 × 216 mm 13.8 × 21.6 cm | 5.43 × 8.50 | 5.5 × 8.5 in (1.7 mm wider) | Trade paperbacks, fiction hardbacks |
| A5 | 148 × 210 mm 14.8 × 21.0 cm | 5.83 × 8.27 | None (5.5 × 8.5 or 6 × 9 in are closest) | Self-printed books, workbooks |
| American Royal | 152 × 229 mm 15.2 × 22.9 cm | 6 × 9 | 6 × 9 in | Non-fiction, US trade paperback |
| Royal | 156 × 234 mm 15.6 × 23.4 cm | 6.14 × 9.21 | 6.14 × 9.21 in | Non-fiction hardbacks |
| Crown Quarto | 189 × 246 mm 18.9 × 24.6 cm | 7.44 × 9.69 | 7.44 × 9.69 in | Illustrated non-fiction, cookbooks |
| A4 | 210 × 297 mm 21.0 × 29.7 cm | 8.27 × 11.69 | 8.27 × 11.69 in | Workbooks, manuals |
UK sizes are from Biddles’ size table and the Wikipedia Book size article (C-format). Printers round these slightly differently; UK Book Publishing lists A-format as 110 × 178 mm, for example. Bold KDP sizes match the UK format within about half a millimetre.
Want to compare any two sizes at full scale on your own screen? The trim size visualiser draws every KDP size side by side.
Which size should your book be?
Pick the size readers in your genre already hold. Take three bestsellers in your category off a shop shelf and measure them; that tells you more than any rule. As a starting point:
| Book | UK convention | KDP size to choose |
|---|---|---|
| Novel, memoir | B-format paperback | 5.06 × 7.81 in, or 5 × 8 in / 5.5 × 8.5 in |
| General non-fiction | Demy or B-format | 5.5 × 8.5 in or 6 × 9 in |
| Business, how-to, textbook | Royal or 6 × 9 in | 6 × 9 in or 6.14 × 9.21 in |
| Cookbook, illustrated non-fiction | Crown Quarto | 7.44 × 9.69 in or 8 × 10 in |
| Picture book | Square or landscape | 8.5 × 8.5 in, 8.25 × 8.25 in or 8.25 × 6 in |
| Workbook, journal | A4 or 8.5 × 11 in | 8.27 × 11.69 in (A4) or 8.5 × 11 in |
Two things decide more than taste:
- Page count. A bigger page fits more words, so the same manuscript prints on fewer pages. On KDP a black-and-white paperback over 110 pages costs £0.85 plus £0.010 a page to print in the UK, so a smaller page count means a cheaper copy and a better royalty. Our word count to page count tool shows how many pages your manuscript will make at each size, and the KDP royalty calculator shows what you earn per copy.
- Distribution. KDP’s Expanded Distribution (to bookshops and libraries) is only open to certain combinations of trim size and paper. If you want UK bookshops to be able to order the book, check KDP’s list before you commit, or read KDP vs IngramSpark for UK authors first. KDP’s own list shows 8.25 × 6, 8.25 × 8.25 and 8.25 × 11 in are not eligible with any paper, 6 × 9 in is eligible with all of them, and hardcovers are not eligible at all.
Amazon KDP sizes in mm and cm
KDP’s size menu is in inches. Here are its paperback sizes converted, with the most pages each takes on black-and-white paper (from KDP’s Set Trim Size page, read 22 September 2026):
| KDP size (in) | Size in mm and cm | Max pages, white paper | UK name |
|---|---|---|---|
| 5 × 8 | 127 × 203.2 mm 12.7 × 20.3 cm | 828 | |
| 5.06 × 7.81 | 128.5 × 198.4 mm 12.9 × 19.8 cm | 828 | B-format |
| 5.25 × 8 | 133.4 × 203.2 mm 13.3 × 20.3 cm | 828 | |
| 5.5 × 8.5 | 139.7 × 215.9 mm 14.0 × 21.6 cm | 828 | ≈ Demy |
| 6 × 9 | 152.4 × 228.6 mm 15.2 × 22.9 cm | 828 | American Royal |
| 6.14 × 9.21 | 156 × 233.9 mm 15.6 × 23.4 cm | 828 | Royal |
| 6.69 × 9.61 | 169.9 × 244.1 mm 17.0 × 24.4 cm | 828 | |
| 7 × 10 | 177.8 × 254 mm 17.8 × 25.4 cm | 828 | |
| 7.44 × 9.69 | 189 × 246.1 mm 18.9 × 24.6 cm | 828 | Crown Quarto |
| 7.5 × 9.25 | 190.5 × 235 mm 19.1 × 23.5 cm | 828 | |
| 8 × 10 | 203.2 × 254 mm 20.3 × 25.4 cm | 828 | |
| 8.25 × 6 | 209.6 × 152.4 mm 21.0 × 15.2 cm | 800 | Landscape |
| 8.25 × 8.25 | 209.6 × 209.6 mm 21.0 × 21.0 cm | 800 | Square |
| 8.5 × 8.5 | 215.9 × 215.9 mm 21.6 × 21.6 cm | 590 | Square |
| 8.5 × 11 | 215.9 × 279.4 mm 21.6 × 27.9 cm | 590 | US Letter |
| 8.27 × 11.69 | 210 × 296.9 mm 21.0 × 29.7 cm | 780 | A4 |
KDP hardcovers come in five sizes: 5.5 × 8.5, 6 × 9, 6.14 × 9.21, 7 × 10 and 8.25 × 11 in, with 75 to 550 pages. The hardcover vs paperback guide has the printing costs.
Chosen your size? We'll set the book to it.
We format your interior to the exact KDP trim, margins and page count, and you see every page before you pay. Paperback from £69, paperback and Kindle £119.
See formatting pricesTrim size is not your Word page size
The trim size is the finished size of the printed book after it is cut. Your document has to be set to that size before you format anything, because changing the page size later reflows every line and changes the page count.
If any page has pictures or colour running to the edge, the whole interior needs bleed: 0.125 in (3.2 mm) extra on the top, bottom and outside edges. A 6 × 9 in book with bleed is set up as a 6.125 × 9.25 in page and uploaded as a PDF. Every KDP cover needs bleed.
The inside margin (the gutter) grows with page count, so the words don’t disappear into the spine. KDP’s minimums:
| Page count | Inside margin | Outside, no bleed | Outside, with bleed |
|---|---|---|---|
| 24–150 | 0.375 in / 9.6 mm | 0.25 in / 6.4 mm | 0.375 in / 9.6 mm |
| 151–300 | 0.5 in / 12.7 mm | 0.25 in / 6.4 mm | 0.375 in / 9.6 mm |
| 301–500 | 0.625 in / 15.9 mm | 0.25 in / 6.4 mm | 0.375 in / 9.6 mm |
| 501–700 | 0.75 in / 19.1 mm | 0.25 in / 6.4 mm | 0.375 in / 9.6 mm |
| 701–828 | 0.875 in / 22.3 mm | 0.25 in / 6.4 mm | 0.375 in / 9.6 mm |
These are minimums, not targets. Running heads and page numbers count as text, so a file set exactly at the minimum can still be bounced; we set every book comfortably inside them. The KDP margin calculator works out yours.
The cover follows the size
Once you know the trim size and page count, the cover size is fixed: two panels the size of your trim, a spine that depends on the paper, and 0.125 in bleed all round. The KDP cover calculator gives the full size in inches, mm and pixels and downloads a template at 300 DPI.
Frequently asked questions
What is the standard size of a paperback book in the UK?
There are three. A-format is 111 × 178 mm (the small mass-market paperback), B-format is 129 × 198 mm (the familiar paperback novel size, used by Penguin Classics) and C-format or Demy is about 135–138 × 216 mm for larger trade paperbacks.
What size is an A5 book?
148 × 210 mm, which is 14.8 × 21 cm or 5.83 × 8.27 in. Amazon KDP does not offer A5. The nearest KDP sizes are 5.5 × 8.5 in (140 × 216 mm) and 6 × 9 in (152 × 229 mm). UK printers such as Biddles list A5 as a standard size if you are printing copies to sell yourself.
What is the most common book size on Amazon KDP?
For text-led books, 5 × 8 in, 5.06 × 7.81 in (UK B-format), 5.5 × 8.5 in and 6 × 9 in. Novels usually go smaller; non-fiction with tables and headings usually uses 6 × 9 in.
What size is a hardback book in the UK?
Usually Demy (138 × 216 mm) for fiction and Royal (156 × 234 mm) for larger non-fiction. KDP’s hardcover sizes include 6.14 × 9.21 in, which is Royal.
What size is a 6 x 9 book in cm?
15.24 × 22.86 cm (152.4 × 228.6 mm). The UK trade calls it American Royal.
Does book size change the price of printing?
Yes, through the page count. A bigger page fits more words, so the book has fewer pages. KDP charges a fixed amount plus a charge per page, so fewer pages makes each copy cheaper.
Sources
- Biddles, standard book sizes: https://www.biddles.co.uk/book-printing/book-sizes-info/ (read 30 September 2026)
- Wikipedia, Book size (UK paperback formats): https://en.wikipedia.org/wiki/Book_size (read 30 September 2026)
- Amazon KDP, Set Trim Size, Bleed, and Margins: https://kdp.amazon.com/en_US/help/topic/GVBQ3CMEQW3W2VL6 (read 22 September 2026)
- Amazon KDP, paperback printing cost: https://kdp.amazon.com/en_US/help/topic/G201834340
- Amazon KDP, Expanded Distribution eligibility: https://kdp.amazon.com/en_US/help/topic/GQTT4W3T5AYK7L45 (read 30 September 2026)
Who wrote this. I am Robert Prime. I run publishing.co.uk, a UK book formatting service, and choosing the trim size is the first question on every book we set. The UK sizes come from a UK printer's own table, and the KDP sizes from Amazon's help pages; the millimetre conversions are our own arithmetic. If a printer or KDP disagrees with a figure here, they are right: tell me and I will correct it.
