Page Margin Calculations
Updated: Nov 12, 2020
I was trying to come up with a clever name for the title, but failed.
When designing a trade book, for example a novel, the very first thing that needs to be worked out after the page dimensions have been decided are the margins of the page. Unlike a magazine, we look at the spread of the book, ie the left and right pages together. I like to call the right-hand page the recto and the page on the left the verso.
So with the recto and verso in front of you, you will have spread as shown below.
Traditionally the outside margin o is twice that of the inside margin i. That means that the each column of white space is equal, ie the o on the verso = 2 × i = the o on the recto.
There are various systems in calculating the margins around the page. My favorite is the above. The top and inside ( i ) margin are 1/9 of the width of the page and the outside ( o ) and bottom margin are double that. These values can be tweaked to fit with the grid of the page. The position of the running heads and folios (page numbers) might also affect the top and bottom margins. So for a book that has the folios and running heads at the top with nothing below, the top margin might be increased at the expense of the bottom margin. It is important that there is ample footer space, not just for aesthetic reasons, but to allow the text box to be lengthened by a line in order to align the bottom of the recto and verso (“balancing”).
There is another factor to consider. The width of the text box, known as the measure should be such that it contains on average 65 characters. So now we have to make sure that the typeface chosen in the font size that is desired will be appropriate for the measure. We certainly don’t want to have a book with a measure of 130 characters (including spacing).
Sometimes, this requires reevaluating the dimensions of the book to allow appropriate margins for the text size chosen.
There is however a new factor that we have to take into account and that is of the printing process. We will address this shortly, but it is worth mentioning mass-market books where all the above concepts are thrown out of the window in favor for economy.
Many (or perhaps most) books that we read, fall into the category of mass-market books. Here every millimeter of space is precious to manufacture the book as cheaply as possible. In such a book the margin around the text book will be very small indeed possibly as little as 5mm.
The Printing Process
So ignoring the above category of books as book designers, we have to take into account how the book is going to be printed. In the below picture, we have a paperback book which has been smyth-sewn. As a result the book is what is known as a lay-flat book.
The inside margins reflect what we would set up in InDesign. On the other hand, many paperback books will look more like this:
Note how there is a significant curvature in the spine and this has to be taken into account when working out the inner margins. After all, the goal is for the outside margin to equal the space in between the text block of the recto and verso. Visually we are going to see what the ruler above is going to see in this position. So we need to compensate for that. Another problem is that many printing presses might shave off up to 3 mm of the width of the book and they typically shave off from the spine so it’s the inside margin that suffers.
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