Reference
Book margins
Margins are the white space around the text block, and in a printed book they are not symmetrical. The margin at the fold has to be wider than the one at the outer edge, and how much wider depends on how thick the book is.
That single asymmetry is what most first-time formatters get wrong, and it is visible in the finished book.
The four margins
- Inside (gutter)
- At the fold. The widest of the four, and the one that grows with page count.
- Outside
- At the outer edge, where the reader's thumb goes. Wider than the printer's minimum is worth it for that reason alone.
- Top (head)
- Above the text block, below the running head.
- Bottom (foot)
- Below the text block. Traditionally slightly larger than the top.
Because the inside margin is the one at the fold, it swaps sides on every page. This is what a formatting tool means by mirrored margins, and it is why setting a single left margin for the whole book produces a book that is wrong on half its pages.
The minimums, by page count
KDP publishes an inside-margin minimum that increases in bands. These are the printer's requirements — a file below them is rejected, not merely criticised.
| Page count | Minimum gutter | Metric |
|---|---|---|
| Up to 150 pages | 0.375 in | 9.5 mm |
| 151 – 300 | 0.5 in | 12.7 mm |
| 301 – 500 | 0.625 in | 15.9 mm |
| 501 – 700 | 0.75 in | 19.0 mm |
| 701 – 828 | 0.875 in | 22.2 mm |
Outside, top and bottom must each be at least 0.25 in — or 0.375 in if the interior uses bleed.
The trap is the band boundary. A book at 298 pages needs 0.5 in; add three pages in a revision and it needs 0.625 in, which changes the measure, which repaginates the book. Check the requirement against the FINAL page count, not the draft one.
IngramSpark and other printers
IngramSpark publishes its own minimums, and they are not identical to Amazon's. If you are printing through both, set your margins to satisfy whichever is stricter for your page count rather than maintaining two interiors.
The general principle holds everywhere: check the requirement against your specific printer, your specific trim and your final page count. Every printer publishes a template generator, and the template is always the authority over any table, including this one.
Beyond the minimum
Meeting the minimum gets your file accepted. It does not make the book look good. What separates a competent interior from a compliant one:
- Generous outside margins. This is where the reader's thumb rests, and where the eye finds the line ending.
- A measure of 60–75 characters. Margins and type size together determine this, and it matters more than either alone.
- A bottom margin slightly larger than the top, so the text block sits optically centred.
- Consistent margins throughout. Front matter can breathe more, but the body text block must not move from page to page.
Questions, answered
What is a gutter margin?
The inside margin — the one at the fold, where the pages are bound. It has to be wider than the outside margin because part of it curves into the binding and is not fully readable. On a left-hand page it is the right-hand margin; on a right-hand page it is the left. That reversal is what mirrored margins means.
What margins does KDP require?
Outside, top and bottom must be at least 0.25 in, or 0.375 in if your interior uses bleed. The inside margin depends on page count: 0.375 in up to 150 pages, rising in bands to 0.875 in beyond 700. These are minimums, not recommendations.
Why does the gutter get bigger for longer books?
A thicker book has a stiffer spine and does not open as flat, so more of the inner margin curves away from the reader. A 700-page book with a 0.375 in gutter has text disappearing into the fold. The bands exist because that effect scales with thickness.
What margins should I actually use?
More than the minimum. For a 6" × 9" novel, something like 0.875 in inside and 0.75 in outside, with 0.75–1 in top and bottom, looks like a book. Books set at the printer's minimum read as cramped even when nothing is technically wrong.
Should the top and bottom margins be equal?
Traditionally the bottom margin is slightly larger than the top — it makes the text block look optically centred rather than sitting low on the page. Equal is fine and nobody will complain; a top margin larger than the bottom looks wrong to almost everyone, without their being able to say why.
Do ebooks have margins?
Not ones you control. The reading app sets them, and readers can usually adjust them. Setting fixed margins in your EPUB's CSS fights the reader's own settings and is one of the more common ways an ebook is made worse by effort.
Have the margins checked for you
Alhora checks your margins against the band your real page count falls into, and re-checks when the page count crosses a boundary — which is the moment a compliant book quietly becomes a non-compliant one.
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