Margins and gutters
Ask why a page has margins and most people answer that it looks better. That is the smallest part of it. The margin is where your thumbs go, it is the white that gives the type room to breathe, and above all it is the buffer that stops the last word of every line vanishing into the spine.
Margins are also the single decision that most often gets copied from the wrong place — a template built for a different trim size, or a default that was never chosen at all.
The four margins are not equal
A word processor gives you four equal margins and calls it done. A book page does not work that way.
- Inside is larger than outside. The inside margin is consumed by the binding; the outside is not. Equal margins on a bound page look wrong because the inside one is not all there.
- The foot is larger than the head. Traditional page design puts more space at the bottom than the top, often noticeably so. Center the text block vertically and the page looks like it is sliding off the bottom — an optical effect, but a reliable one.
- The margins mirror. Left-hand and right-hand pages are reflections of each other, so the inside margin is on the right of a left-hand page and the left of a right-hand page. Without mirroring, every second page sits visibly off-center.
The gutter grows with the page count
The gutter is the extra inside margin that accounts for the binding. It is not a fixed number, because a thicker book curves harder at the spine: a 200-page paperback lies nearly flat, a 700-page one does not, and the same inside margin that was generous in the thin book is swallowed in the thick one.
These are working figures for the total inside margin, by final page count:
| Page count | Inside margin |
|---|---|
| Up to 300 | 0.5" |
| 301–500 | 0.625" |
| 501–700 | 0.75" |
| 701–828 | 0.875" |
| More than 828 | 1.0" |
Note the order of operations here. You cannot set the gutter until you know the page count, and you do not know the page count until the book is typeset — which is why the gutter has to be set from the real, composed page count rather than an estimate made at the start.
Build to the larger floor
Print services publish different minimums. KDP will accept an inside margin as small as 0.375" on a short book. IngramSpark's floor is 0.5".
Build to 0.5" and above and you have one interior file that is valid at both. Build to KDP's minimum and you have a file you will have to reset the day you decide to go wide, and by then your page count — and therefore your spine width and your cover — will change with it. The extra eighth of an inch costs you almost nothing and buys you a book you can print anywhere. See Where to print.
In the Interior Formatter. The gutter is set from the composed page count, not a guess — so a 540-page book gets the 0.75" inside margin it needs, and the final count flows straight to the Cover Maker so the spine matches. Start a book → · about the Interior Formatter
What too-small margins look like
You have seen this book and probably could not name what was wrong with it.
Text curves down into the spine and you have to press the pages flat with a thumb to read the end of each line. The page is dense edge to edge, with no quiet border to rest the eye against. Nothing is technically illegible, and readers do not report "the inside margin is 0.3 inches." They report that it was hard to read, or tiring, or that it felt self-published.
What too-large margins cost
The opposite error is real, and it is expensive.
Every inch of margin you add takes lines off the page, which adds pages to the book. More pages means higher print cost per copy, and on a print-on-demand title that comes straight out of your royalty on every single sale. More pages also means a thicker spine, which changes your cover.
A book padded out with huge margins reads as padded. It does not read as generous.
Scale the margins to the trim size
This is the part templates get wrong. Margins are proportions, not fixed quantities.
Half an inch of outside margin on a 5×8 page is a tenth of the page width. The same half inch on an 8.5×11 page is under a sixteenth, and looks mean. Copy the margins from a 6×9 template into a 5×8 book and the text block is too wide for the line length, so the measure gets long, and long lines on a small page are tiring to read.
Two rules that hold across sizes:
Set the outside margin as a proportion of the page width, so it grows and shrinks with the trim. It is the margin the reader's eye actually registers as "the border."
Set the inside margin from the table above, then add nothing for the trim. The gutter answers to the binding and the page count, not the page size.
Choose the trim first, then the margins, then let the page count tell you the gutter. Doing it in that order means you set each number once. See Choosing a trim size and, for the larger margins a large print edition needs, Large Print edition.
Make yours
Everything here is built into the tools, and they are free to use: name your book, bring your manuscript or your artwork, and work as long as you like. You only pay when you want the files without the preview watermark.
Next: Front matter order · Back to How to format a book interior · Also: Spine width