in Production
Trim sizes and what they tell a reader
Before a reader looks at the cover, the shape of a book has already told them something. Trim size is a design decision, not only a technical one.
Trim size is the finished size of a book's pages after printing and trimming. It is one of the first production decisions and one of the most consequential. It affects the page count, the cost, the feel in the hand and what kind of book a reader assumes it is before reading a word.
Common sizes in the UK
British publishing has a set of long-established formats. Mass-market paperbacks are commonly A-format, about 178 by 111 mm. The standard paperback for much fiction and non-fiction is B-format, about 198 by 129 mm. Larger formats include Demy, about 216 by 138 mm, and Royal, about 234 by 156 mm, often used for hardbacks, larger paperbacks and non-fiction.
American publishing uses sizes measured in inches, with 6 by 9 inches and 5.5 by 8.5 inches among the most common for trade books. Many print-on-demand services offer both sets of sizes, along with others.
Printers can produce almost any size, but standard sizes are cheaper and simpler, because they make efficient use of standard paper sheets and fit existing equipment.
What size signals
Readers make assumptions from format. A small paperback suggests an affordable, portable read, often genre fiction or a reissue. A larger paperback often signals literary fiction or serious non-fiction. A large hardback suggests a significant new book, or a gift. Cookbooks, art books and picture books have their own sizes, often larger and sometimes square or landscape.
These associations vary by market and shift over time, but they are strong enough that a book in an unexpected format can look out of place. A literary novel in a mass-market format may look less serious than intended; a slim poetry collection in a very large format may look thin.
The simplest guide is to look at recently published books in the same category and note their sizes.
How size affects the text
Trim size and page count are linked. The same manuscript in the same type will run to fewer pages in a larger format and more pages in a smaller one. A long novel in a small format can become an uncomfortably thick book; a short one in a large format can look slight.
Size also shapes the reading experience. Line length depends on the width of the text area. A very long line is tiring to read, because the eye struggles to find the start of the next one, while a very short line breaks the text into choppy fragments. Larger formats often use larger type or wider margins to keep the line comfortable. The designer balances type size, line spacing, margins and trim size together, and changing one affects the others.
Practical constraints
Not every size is available with every printing method. Print-on-demand services support a defined list of sizes, and some bindings or paper stocks are only available in certain sizes. Hardbacks and paperbacks may be offered in different sets of sizes.
If a book will exist in more than one edition, such as a hardback followed by a paperback, each may use a different trim size. Each then needs its own interior layout, or at least a careful check that the existing layout still works.
Choose the trim size early. Changing it after the interior has been typeset means resetting the whole book, and a new page count means a new spine width.