Book Sizes UK & US – Book Printing Guidance

Book sizing: The Ultimate Guide.

Books come in all shapes and sizes and if you are considering self-publishing, you are confronted with the choice of exactly what size your book should be. Considering all the different options can be daunting. However, if you understand a few basic factors and features, choosing the right book size should be easy.

You might be wondering why choosing the right book size is so important. As long as it fits on the shelf right? Not really! Your book size will affect how you go about typesetting or formatting your manuscript. It will also have an impact on your audience’s reading experience, and it can have a big impact on your pocket. It is therefore important to understand how sizing works. 

Books sizes have traditionally varied based on a variety of factors including economic, practical and aesthetic considerations. In this guide, we help you understand the most important things to think about when it comes to book sizing in order to help you along in your self-publishing journey.

First things first: Trim size v Cover Size

Trim size is publishing speak for book size. The trim size refers to the last stage of production – after the book is printed and bound, the book is mechanically trimmed so that all the page sizes are uniform. 

Paperback books will have the same trim size and cover size. However, when it comes to hardback books, the trim size refers to the inner book block and not the outside of the case or cover. The cover or the hardcase always extends past the interior pages on all sides. If you are considering a hardcover, it’s important to remember this.

It is also important to note that in the UK and Europe, trim size is denoted in millimetres as the metric system is used whilst in the US it’s denoted in inches. What is more, standard book sizes differ depending on your location – they aren’t consistent across the world. For example, the UK has a whole different set of ‘standard sizes’ than the US. The location of your self-publishing system or print on demand printer will therefore determine what standard sizes are available to you. A little more on this later. For now, let’s have a look at the most important factors to consider.

Important Factors

There are a number of websites that provide lists of book sizes, tables, and other helpful information when it comes to book sizing. However, being confronted with a list of sizes won’t make your decision easier. The factors below are all that you need to consider in order to find the right book size for your book.

Financial implications

It is important to remember that the trim size of your book will determine your page count. The smaller your trim size, the more pages your book will consist of. Because of this, if you are charged based on page count, the more pages in your book, the more the printing cost will be and possibly the smaller your profit margin.

Although a cheaper print might sound like a good idea, you need to balance the cost with other factors, such as your target audience, genre and practicality.

Practical considerations

As the trim size determines your page count, it will also determine the number of words on the page and the size of the margins. The page trim together with these factors will need to be balanced in order to ensure a beautiful and practical book.

What is more, page trim will also determine the thickness of the spine of the book. A thicker book might look substantial on the shelf, but it is clunkier and might be difficult to handle physically. 

Therefore, you have to think about your target audience. Think about how the book will be used physically. Does it need to fit into a carry on or a handbag? Does it have tables, diagrams or illustrations that need to be larger in order to be legible? Is it a cookbook that needs to be a durable premium product? Is it a textbook or academic book that will be used on a desk and over and over again? All of these practical considerations are extremely important in order for your book to succeed. These factors will also have an impact on how much your book will cost to ship as well as its ability to be displayed on the shelf in bookstores.

When thinking about practicality, the easiest way to make the right decision is to look at other books in your genre.


Standard book sizes used by the publishing industry give you the best clue on how to choose the size for your book. Look at the typical book sizes for your genre and the sizes you particularly like for books in that genre.

Choosing an industry standard will ensure that your book looks as professional as possible. Choosing a genre standard means that readers will immediately recognise your book as a legitimate edition.

If you plan to deviate from the industry or genre standard, you need to have a good reason. Although you might want to stand out, a differing book size might have the inverse effect and alienate your target audience – readers might not recognise your book for its specific genre. It might also result in it being difficult to display, which could result in it being poorly displayed by retailers. The best way to ensure your book’s marketability is to meet your target audience’s expectations.

Paperback vs Hardback – Best binding for your project?

Choosing the right binding for your book is another choice that you will be confronted with. Although the choice between a hardcover and paperback is a subjective one, you need to consider the above-mentioned factors.

Apart from considering cost, marketability and genre, here a few more things take into account when choosing between a hard and soft cover:

Hardcover Book Benefits Paperback Book Benefits
  • They are durable and have a longer shelf-life than paperbacks.
  • Aesthetically, they are more attractive.
  • The cost of production is higher. 
  • Should seriously be considered if you are writing a textbook, book for reference, workbook or cookbook.
  • They make great gifts and are bought for that purpose.
  • Higher shipping costs – with a heavier weight and a larger book size, the shipping costs will be more.
  • They are cheaper to produce.
  • They do not last as long as hardcovers.
  • They are probably the most popular binding type.
  • They are easier to carry.
  • Should seriously be considered if you are writing a book that you want to be highly portable. 
  • Easily distributed. Paperback books are accepted worldwide by almost every bookshop and book distributor.

The most popular book sizes

Remember, standards aren’t consistent across the world. In this section, we highlight the most popular standards in the UK and the US with the help of If you are in another region, any good printing company or publisher will be able to shed light on a specific country’s industry standards. 

As mentioned, UK sizes are all metric while US sizes are in inches.

Most popular book sizes UK

Book Format Name

Book Format Dimensions



178 mm X 111mm This format is perfect for travellers and readers on the go. It is widely used for reprints of classic novels and niche fiction and is used as the standard for airport fiction.


198 mm X 129mm B-format books are likely the most widely circulated in the UK. They are the industry standard for most paperback fiction and is a solid option to choose. They are widely stocked in physical bookstores as well as online and most print-on-demand companies will have the B-format as a standard recommended size.

The Demy

216mm X 135mm The demy is used for large-format paperbacks instead of hardbacks that are more expensive to produce. It often replaces the more traditional A-format. It is a good option for a mass-market book as it attracts attention on the shelf without the high cost of printing a hardback.

The Royal

234 mm X 156mm The royal is a long-format size used for more superior novels and some non-fiction, such as autobiographies. Although the royal is usually available in paperback format, it very often has a hard cover. This format is more expensive to produce but has a big visual impact on the shelf.


Most popular book sizes US

Book Format Name

Book Format Dimensions


The pocketbook

4.25 X 6.87 inches Pocket books fits snugly into the back pocket. They are easy to carry around and cheap to print and as such they are used for cheaper paperback fiction. They are to be found in airports, newsagents and bookstores.


5.5 X 8.5 inches The digest is the smallest format of what are termed ‘trade sizes’ in the US. They are widely circulated and is suitable for both fiction and non-fiction titles.

US Trade

6 X 9 inches This is a slightly larger format than the digest and is used for paperback fiction. It is a safe size to consider for fiction and is a standard size offered by most print-on-demand services.


ranges from 6 X 9 inches to 805 X 11 inches Hardcovers vary widely in size in the US. It is a more expensive option but is becoming increasingly popular.

Summary List of all Popular Book Sizes, in Metric Dimensions

Book (trim) size Height x Width
  A6 148 x 105mm
  A Format 178 x 111mm
  B Format (UK) 198 x 129mm
  B Format (US) 203 x 127mm
  A5 210 x 148mm
  Demy 216 x 138mm
  American Royal 229 x 152mm
  Royal 234 x 156mm
  Pinched Crown Quarto up to 248 x 171mm
  Crown Quarto 246 x 189
  A4 297 x 210mm

So which book size is right for you?

If what you are looking for is maximum flexibility, book printers suggest that it is a good idea to pick a UK standard that has the approximate equivalent of a US standard. For example, the US 6″ x 9″ standard (152mm x 229mm) is the rough equivalent of the UK “Royal” size (156mm x 234mm). For a slightly smaller size, the UK “Demy” size (138mm x 216mm) is a good match for the common US “Digest” size of 5.5″ x 8.5″ (140mm x 216mm).

It is also important to note that the US also has a B-format size. The UK B-format (210 × 135mm / 8.26 × 5.31 inches) is slightly larger than the US B-format (198 × 129mm /7.79 × 5.07 inches). The B-format is the most popular paperback around the world and is suitable for fiction books, poetry and novels. The B-format, in general, has a lower production cost and are accepted in almost every bookshop and every book distributor.

At Undercoverprint, we offer a range of sizes that suit most authors’ needs, including the standard sizes as well as some other options such as the Crown Quatro used in education and training documents; the B5 that is very popular with journal publishers; and the A4 and A5 used across a range of subjects, including novels, guidebooks, and children’s books. If you are ready to start planning the size of your book, have a look at our sizes on offer and do not hesitate to contact us for advice and a competitive quotation.

It is important to remember that although you can basically print your book in any size you want, the most important considerations boils down to cost, industry and genre standard, and practicality.