Choosing the right size of book isn’t just about aesthetics. It affects everything from production costs to how your readers experience your work. Drawing on years of industry expertise, this comprehensive guide covers every standard UK book size — paperback and hardback — in millimetres, centimetres and inches, with an actual-size picker so you can see each format before you commit.
See every UK book size at a glance
Trim sizes are hard to picture from millimetres alone. Click through the standard UK formats below — each is drawn to the same scale, with a bank card as a real-world reference, so you can see exactly how A-format compares to Royal or A4 before you commit. Each size links straight through to price a book in that format.
Standard UK book sizes: the complete chart
The industry recognises a handful of standard book sizes, used across both paperback and hardback book printing. Here is every standard UK trim size — the same chart in millimetres, centimetres and inches:
| Size (name) | Millimetres | Centimetres | Inches | Typically used for |
|---|---|---|---|---|
| A6 (pocket) | 148 × 105 | 14.8 × 10.5 | 5.8 × 4.1 | Pocket guides, poetry, gift books |
| A-format | 178 × 111 | 17.8 × 11.1 | 7.0 × 4.4 | Mass-market fiction |
| B-format | 198 × 129 | 19.8 × 12.9 | 7.8 × 5.1 | The UK fiction standard |
| Demy | 216 × 138 | 21.6 × 13.8 | 8.5 × 5.4 | Memoir, biography, trade non-fiction |
| A5 | 210 × 148 | 21.0 × 14.8 | 8.3 × 5.8 | Non-fiction, manuals, journals, poetry |
| Royal | 234 × 156 | 23.4 × 15.6 | 9.2 × 6.1 | Textbooks, business and reference |
| B5 | 250 × 176 | 25.0 × 17.6 | 9.8 × 6.9 | Academic and technical books |
| A4 | 297 × 210 | 29.7 × 21.0 | 11.7 × 8.3 | Manuals, cookbooks, photography, children’s |
| Square | 210 × 210 | 21.0 × 21.0 | 8.3 × 8.3 | Children’s picture books, photo and art books |
All dimensions are the trim size — height × width of the finished, bound book, which is also the book’s page size. Custom sizes between these are also possible: we print anything from 105×145mm up to 310mm square.
How are books measured?
Three measurements describe every book, and the size names above refer to the first:
- Trim size (= page size): the final height × width of the book after it’s been bound and trimmed. When someone asks “what size is a book page”, this is the answer — the page and the trim are the same size. Every dimension in this guide is a trim size.
- Spine thickness: how thick the book is — set by page count, paper and binding, and always quoted in millimetres. Our spine calculator returns it for any spec.
- Cover dimensions: the physical outside of the book. On a paperback the cover is trimmed flush, so it matches the trim size; on a hardback the boards overhang — see the hardback section below.
Trimming happens after the binding process, once the cover is attached to the book block — which is why the trim size is the definitive “size of the book”.
What’s the average size of a book?
For UK adult books the practical answer is 198 × 129mm (B-format) for fiction and 210 × 148mm (A5) or 234 × 156mm (Royal) for non-fiction — a “typical” book on a UK shelf falls between 178mm and 234mm tall. If you’re unsure, those three sizes cover the overwhelming majority of new titles.
Hardback book sizes: trim, case and jacket
Hardback trim sizes are the same as paperback ones — a B-format hardback and a B-format paperback share identical page dimensions, and every size in the chart above is printed in both formats. What changes is the outside of the book:
- The boards overhang the pages. A hardback’s cover boards are cut larger than the trimmed page block — the overhang is called the square. Our cases carry a 5mm square at the fore-edge and 3mm at head and tail, so a finished hardback is roughly 5mm wider and 6mm taller than its trim size: a 198×129mm B-format hardback measures about 204mm tall × 134mm wide over the boards.
- The spine is thicker. Boards, endpapers and the case add several millimetres to the spine over the equivalent paperback — the spine calculator quotes cased and paperback spines separately.
- A dust jacket adds flaps, not size. A jacketed hardback is the same finished size; the dust jacket is cut to wrap the case exactly, with (typically 90mm) flaps folding inside the boards.
Two practical consequences: shelf and box space is set by the case size, not the trim; and cover artwork for a hardback is built to the board dimensions, not the page — which is exactly what our free cover template generator lays out for you (paperback, hardback PPC and dustjacket formats). For everything else that changes with the format, see hardback book printing and our hardcover vs paperback decision guide.
UK book size names, explained one by one
What size is an A-format book?
A-format is 178 × 111mm (7 × 4.4 inches) — the classic mass-market paperback: airport thrillers, romance and film tie-ins. It’s the most economical size to print and post at very large volumes, with the trade-off of a dense page.
What size is a B-format book?
B-format is 198 × 129mm (7.8 × 5.1 inches) — the standard UK paperback size for literary and general fiction. If you pick a novel off a UK bookshop table, this is most likely its size, which makes it the safest default for self-published fiction.
What size is a Demy book?
Demy is 216 × 138mm (8.5 × 5.4 inches) — a traditional British trade size sitting between B-format and Royal. It’s a popular choice for memoir, biography and serious non-fiction, and for hardback fiction.
What size is an A5 book?
A5 is 210 × 148mm (8.3 × 5.8 inches) — exactly half an A4 sheet, and the workhorse of self-publishing: non-fiction, manuals, workbooks, poetry and journals. Its familiar proportions and efficient use of the printed sheet make it one of the most cost-effective sizes to print.
What size is a Royal book?
Royal is 234 × 156mm (9.2 × 6.1 inches) — the larger UK trade size, close to the American 6×9-inch trade paperback. It suits textbooks, business books and substantial non-fiction, and it carries more words per page, so long manuscripts make fewer pages at Royal than at B-format or A5 — try it in the words-to-pages tool.
What size is a B5 book?
B5 is 250 × 176mm (9.8 × 6.9 inches) — a generous format for academic, technical and heavily illustrated non-fiction where tables, figures or two-column layouts need room to breathe.
What size is an A4 book?
A4 is 297 × 210mm (11.7 × 8.3 inches) — the largest standard format, used for manuals, reports, cookbooks, photography books and children’s titles. In landscape orientation it’s also a strong choice for portfolios and picture books.
Standard sizes by type of book
What is the standard size of a paperback book?
If you are producing a standard fiction book, then you can be safe to set your book in one of the more common book sizes: either B-format (198×129mm – 7.8×5.07 inches) or A5 (210×148mm – 8.26×5.82 inches). There is no set standard paperback size for all books, as the size differs with genre and market.
What is a mass-market paperback?
A mass-market paperback book is a smaller and more affordable type of paperback compared to regular paperback books. These books use cheaper paper and simpler cover finishes to keep production costs low, and are typically printed in very large quantities — which is what makes them economical. In the UK the mass-market size is A-format (178×111mm). Their compact size also makes them easy to carry.
What size are trade paperback books?
Trade paperback books are normally the same size as their hardback equivalent but without the hard cardboard cover. They will have a thicker cover than a mass-market paperback book, giving you the nice, larger-format book without the bulk and weight of the hardback. Trade paperback sizes usually run from 229×152mm (9×6 inches) up to 279×216mm (11×8.5 inches); children’s picture books tend to sit around 254×203mm (10×8 inches).
What size should my hardback book be?
If you’ve already published a paperback edition, work from the paperback size — hardback trim sizes are based on their paperback equivalents, and one interior file serves both. Popular hardback sizes run from B-format and Demy (fiction) through Royal (non-fiction) up to 279×216mm (11×8.5 inches) for illustrated work; larger than that is normally reserved for picture and art books. Remember the case adds its overhang on top of the trim (see the hardback section above).
What is the standard fiction book size?
Fiction books come in all different shapes and sizes. Mass-market paperbacks (A-format, 178×111mm) save on production and shipping costs at very large print runs. B-format (198×129mm / 7.8×5.1 inches) is the standard UK fiction size — the size most literary and general novels on a UK bookshop shelf are printed at. A slightly larger 210×135mm variant (sometimes called B+ or trade) is also common for début hardback fiction’s paperback editions.
What is the standard non-fiction book size?
Non-fiction books come in a wide range of sizes, often more varied than fiction titles. When choosing, a good approach is to visit local bookshops and browse titles within your genre, noting their dimensions. Popular non-fiction sizes are A5 (210×148mm), Royal (234×156mm), B5 (250×176mm) and A4 (297×210mm).
What is the standard children’s book size?
Children’s book sizes are generally determined by the age of the reader. For babies and toddlers up to 2 years old, smaller formats around 190×190mm (7.5×7.5 inches) work best. For ages 2 to 5, a typical size is 178×254mm (7×10 inches). From age 5 onwards, larger formats such as 254×203mm (10×8 inches) give illustrations and text room to breathe — see our children’s book printing for the formats we produce.
What are the standard photo book sizes?
Photo books tend to be large hardback formats — aim for upwards of B5 (250×176mm). See our coffee-table book printing for the larger photographic formats we produce.
What is the standard portfolio book size?
Portfolio books sit close to photo books but slightly smaller, since they’re not necessarily all about full-bleed images. A4 landscape (297×210mm) shows work at its best; B5 (250×176mm) is a neat, carryable alternative.
What is the standard pocketbook size?
Pocketbook sizes are, as the name suggests, something you can fit in your pocket: think A6 (148×105mm), or a little taller at a similar width — 229×137mm is a popular UK size for map books.
What are the standard comic book sizes?
A standard comic book is 257×168mm (10.11×6.61 inches), though graphic novels range up to 381×254mm (15×10 inches) where the artwork earns it.
Regional differences: UK vs US book sizes
UK and US publishing name their sizes differently. The American trade paperback (6×9 inches / 229×152mm) sits between UK Royal and Demy; the US mass-market (6.75×4.25 inches / 171×108mm) is slightly smaller than UK A-format; and US print-on-demand platforms list sizes in inches that rarely match UK shelf conventions exactly.
This is especially relevant for authors considering self-publishing book sizes internationally, as distribution partners may expect slightly different dimensions. If you’re printing in the UK and selling in the UK, stick to the UK sizes above.
Print-on-demand sizes
If you’re considering print-on-demand, here’s a snapshot of the sizes offered by some of the major players:
Amazon KDP
- 5″ x 8″ (12.7×20.32 cm)
- 5.06″ x 7.81″ (12.9×19.8 cm)
- 5.25″ x 8″ (13.335×20.32 cm)
- 5.5″ x 8.5″ (13.97×21.59 cm)
- 6″ x 9″ (15.24×22.86 cm)
- 6.14″ x 9.21″ (15.6×23.4 cm)
- 6.69″ x 9.61″ (17×24.4 cm)
- 7″ x 10″ (17.78×25.4 cm)
- 7.44″ x 9.69″ (18.9×24.6 cm)
- 7.5″ x 9.25″ (19.1×23.5 cm)
- 8″ x 10″ (20.32×25.4 cm)
- 8.5″ x 11″ (21.59×27.94 cm)
None of the KDP sizes matches a UK shelf standard exactly — the closest to B-format is 5.06″×7.81″, and the closest to Royal is 6.14″×9.21″. More on the trade-offs in our Amazon KDP printing comparison.
Blurb
Blurb offers sizes tailored to short-run photo books: trade sizes at 13×20cm, 15×23cm and 20×25cm; square books at 13×13cm and 18×18cm; and large formats up to 33×28cm landscape and 30×30cm square.
Shutterfly
Photo-book sizes including 7×9, 8×8, 8×11, 10×10, 12×12 and 11×14 inches — consumer photo formats rather than trade book sizes.
How to choose the best book size for your project
Selecting the right book size is all about balancing form and function. Ask yourself:
- What type of book are you producing?
Fiction, non-fiction, children’s, photo, or comic — each has its ideal dimensions. - What’s your genre?
The genre influences the traditional sizes your readers expect. - Will your book include photographs or detailed graphics?
Larger sizes accommodate higher-resolution images and more intricate layouts. - How do production and shipping costs factor in?
Smaller books may save on costs, while larger books might enhance the reading experience — the book weight calculator shows what any size-and-paper combination weighs, and which postage band a single copy lands in. - Where will your book be sold?
Check local bookshops or competitor titles to see which sizes dominate your market.
Ultimately, the best book size is the one that complements your content and meets your production and distribution needs. Once you’ve picked a size, check your spine with the spine width calculator and generate a production-accurate cover with the free cover template tool.
See how your word count fits each size
The same manuscript makes a very different book at each trim size — an 80,000-word novel is around 240 pages at A5 but closer to 200 at Royal. Try your own word count below, switch between the sizes above, and price the result in one click. (The full tool lives at words to pages.)