Guides

Book margins, gutter and bleed

Margins are the one part of book design that a printer measures and rejects. They are also the part that most decides whether a page looks like a book. Here is what each margin does, what the printers require, and what a typesetter would choose.

The four margins

A page has a top, a bottom, an inside and an outside margin. The inside margin is the gutter. Because the pages of a bound book curve into the spine, the last part of the gutter is hard to see, so it is set wider than the outside margin. On a right-hand page the gutter is on the left; on a left-hand page it is on the right. This is why book margins are mirrored: the two pages of an open spread are reflections of each other, and the text blocks sit slightly toward the outside.

Traditional proportions make the margins unequal on purpose: the top is smaller than the bottom, and the inside is smaller than the outside, so that the two text blocks of a spread read as one unit with a generous frame around them. Print-on-demand reverses the inside rule, because the perfect binding it uses does not open flat, so the gutter needs to be the largest margin.

What the printers require

Amazon KDP measures the margins and rejects interiors under its minimums. The outside margins (top, bottom, outer edge) must be at least 0.25 in, or 0.375 in on a page with bleed. The gutter grows with the page count:

IngramSpark does not publish a table. It recommends 0.5 in of safety on every side and warns when text comes closer. A book that meets KDP's table and keeps 0.5 in outside meets both.

The catch is that the page count is not known until the book is typeset, and it changes with every edit. A 290-page draft that grows to 310 pages during copyedit has just moved into the next gutter band. Check the margins against the final page count, not the first one.

What a typesetter would choose

Minimums are for passing review, not for reading. The margins that make a page look like a book are wider, and they are chosen to give a comfortable measure, the length of a line. Between 60 and 70 characters per line is the range where the eye returns to the next line without hunting. At 11-point type on a 6×9 page, that is a text block about 4.5 in wide, which leaves 1.5 in to split between the inside and outside margins.

The running head and the page number live inside the top and bottom margins, so those margins need room for a line of small type plus a gap. That is why 0.75 in is a better floor than KDP's 0.25 in for a book with running heads.

Bleed

A printer cannot cut a stack of paper to a thousandth of an inch. If an image is meant to reach the edge of the page, it has to be printed slightly beyond the edge so the cut falls inside the ink. That extra strip is the bleed. KDP and IngramSpark both use 0.125 in, on the top, bottom and outer edges only, never on the spine side. A file with bleed is therefore 0.125 in wider and 0.25 in taller than the trim: 6.125 × 9.25 for a 6×9 book.

Two rules follow. First, if nothing touches the edge, do not add bleed; a text-only file at bleed size will be flagged because the text is now inside the bleed area and the margins are wrong. Second, when you do use bleed, the text still has to keep its distance from the trim, and KDP raises the outside minimum to 0.375 in on those pages. Photographs and colored chapter-opener blocks are the usual reasons a novel needs bleed; most never do.

The safe area

The last term you will meet is the safe area or safety margin: how far inside the trim line all text and important detail must stay, whether or not the page bleeds. KDP uses 0.25 in for interiors and 0.125 in for covers; IngramSpark recommends 0.5 in for interiors. Anything closer risks being cut, or simply looks cramped.