Readability 101: Designing the Interior of Your Book

When I tell people I’m a book designer, the response I always get is, “so you design the covers?” And I do—but that’s not the biggest part of my job. It’s the interior design of a book, the text design, that takes the most time—and for good reason.

A book cover is meant to grab the eye while communicating something about the subject matter or nature of the book. It’s a marketing piece! Text design is far less eye-catching—so much so that it’s easy to forget the text is designed at all. This is a good thing.

The text of a book is not meant to attract attention. The design is best executed when it recedes into the background, so the reader is able to read without getting distracted. It may not be the most noticeable or exciting part of the book, but there’s a lot at stake. The text design is the book itself; it holds the book’s meaning. And if the text is poorly designed it will be difficult to read and therefore difficult to enjoy.

So the first purpose of text design is to make the text optimally readable: a book designer wants the reader to read with ease, to avoid eye strain, and to be able to maintain focus and attention. These are achievable goals which make the difference between an engaged and a distracted reader. It all has to do with space, proportion and the eyeball. Text design is also one place in life where it pays to be average. Here are a few considerations that a book designer will be keeping in mind when designing your book:

A good text font:

Not only are there text designers out there designing the insides of books, but there are also type designers out there designing the fonts being used! Professional type designers pay careful attention, over many years, when developing fonts with specific applications in mind. They craft the form of each letter and program it to sit perfectly spaced among the surrounding letters. A readable book will use a professional font designed for text.

Text fonts are generally average in size and shape. Since the eye must be able to recognize letters as letters in order to make sense of them—at a glance, to maintain a steady reading pace—the forms can’t get too funky. Bold, flashy, curly, squished-together, pulled-apart and amateur fonts work in books when used decoratively for a few words at a time (such as in headings), but are fatiguing to read in long blocks. A professional book designer will have access to a library of text fonts that aren’t too fat, aren’t too thin, aren’t too wild, and quietly let the reader get on with reading.

You might be wondering, if average is best, then why isn’t there an ultimate average text font out there—a golden ticket to breezy reading? The simple answer is that there are too many variables for one font to work for everything. Elements such as the line length, the margins, and the size of the page factor into the font choice. Of many solid professional options, some fonts will be more suitable than others in each scenario.

Line length:

The number of words in a line of text dictates the reader’s rhythm of reading. When a line is very short, with few words, the reading experience will be choppy: the eye takes a little break at the end of each line as it moves to the next line, and if a sentence is broken many times before it gets to the point, the reader may lose track of the sentence, and their focus.

With a very long line, the reader’s eye will need a rest before it reaches the line break. Excessively long lines fatigue the eyes, and the reader’s gaze may drift off the page in search of rest, prompting them to put down the book.

As with text fonts, an average line is best: neither fragmented nor overextended, allowing an easy flow of reading that gives the eyes the right balance of information and rest.

Each font, at each size, will have some optimal line lengths—where the spacing looks just right and the line has the right number of words on it. Although there are guidelines for crafting an optimal line, the process of choosing a length is somewhat intuitive: a designer will try a few fonts at a few sizes, examine the spacing of letters on the page, and make adjustments until they hit a sweet spot where the text flows and reading is easy.


The page margins are the blank areas of the page between the page edge and the text. They are perhaps the humblest elements of page design: they’re just empty space! It can be hard to see their value because they aren’t noticeable—but margins strongly impact a book’s readability. They’re like the bumpers that cover the bowling lane gutters at a kid’s party: as the eye travels along a line of text from left to right, it bounces off of the right margin, back to the left margin and winds up at the beginning of the next line, eventually bouncing its way from left to right all the way down the text column.

Margins also have the practical function of leaving space for the hand to hold the book, without blocking the text!

Because margins are so invisible, authors seeking to reduce the page counts of their books often sacrifice them: with small margins, more words can fit on a page! But this can have a big impact on the readability of the book. If the outer margins are too small, the reader’s eye will fall off the edge of the page, and it will be difficult to maintain a flow of reading. If the inner margins are too small, the text of the book will disappear into the fold, and the reader will have to pry the book open in order to read hidden words. The top and bottom margins keep the eye centered on the text, and also allow room for navigation text, such as page numbers. If the page number is crushed up against the body text, it will enter the reader’s field of vision as they read, and cause distraction.

Small margins can disrupt the reading experience, but it isn’t a matter of “bigger is better.” Proportion is important. Although the reading experience is generally more tolerant of large margins, it can be difficult to connect one page to the next if the text is but a few specks in a sea of white. The eye likes to make medium-size leaps, both from line to line and from page to page.

Trim size:

Margins are a great variable to adjust in the search for an easy-reading line—but they can only be adjusted as much as the space on the page allows. The dimensions of the page are defined by the book’s trim size.

A readable book can be created at any trim size, but the choice of trim size does impact the other choices a designer will make—choices about the margins, which impact the line length, which impacts the font choice. There’s no one correct trim size, but there are sizes that lend themselves to different applications.

If a manuscript has large images or sidebars, a large trim size will leave enough room for those elements, without squishing the text into a narrow column. Yet if the text needs to be set in narrow columns, then a font can be chosen that is better suited for a shorter line (newspapers use narrower fonts that fit more words into the short lines of their columns). If the book is straight text in a single column, selecting a smaller trim size will allow a designer to choose medium-size margins for a medium-length line—but if the font size needs to be large, to allow vision-impaired readers to enjoy it, then the lines of text will be a little longer, and the book’s trim size a little larger, to maintain good margins. Changing the font, the margins, or the trim size will almost always call for a change in one of the other spacing variables in the design.


I’ve described some major, defining elements of text design that set the structure of the book. But the spacing and proportional considerations don’t end here: the vertical space between lines of text, the proportions of headings and navigation text to the body text, the incorporation of decorative flourishes, and the integration of lists, tables, images and sidebars all come into play when designing a book. Each variable impacts other variables and must be carefully balanced against them, which makes text design a sensitive and time-consuming process—but one with huge payoff. A well-designed book is an easier, faster and more pleasant read, making it much more likely to stay in the reader’s hand.

Written by Meaghan McAneeley, FriesenPress Designer