Free tool
Book margin calculator
Print margins 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 — because a thicker book curves more at the spine and swallows more of the inner margin.
Enter your page count for both the printer's minimum and a recommendation. They are different numbers and you should see both.
Calculate your margins
0.875 in inside
Recommended for 320 pages (301–500 pages)
- Inside (gutter)
- 0.875 in · minimum 0.625 in
- Outside
- 0.5 in · minimum 0.25 in
- Top
- 0.75 in
- Bottom
- 0.875 in
The minimums are Amazon KDP's published table. IngramSpark and other printers publish their own and they are not identical — check your printer's specification, which is always the authority. The recommendations are ours, and are a starting point rather than a rule.
The four margins
Because the inside margin sits at the fold, it swaps sides on every page. That 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.
Why the gutter grows with page count
A thicker book has a stiffer spine and does not open 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. KDP's requirement therefore steps up in bands:
| 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 |
The trap is the 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, which changes the page count again. Check the requirement against the final page count.
Meeting the minimum is not the goal
The minimums get your file accepted. They do not make the book look like one. What separates a competent interior from a merely compliant one:
- Generous outside margins. This is where the reader's thumb rests and where the eye finds the end of each line.
- A measure of 60–75 characters. Margins and type size together decide this, and it matters more than either alone.
- A bottom margin slightly deeper than the top, so the text block sits optically centred.
- Consistency. Front matter can breathe more, but the body text block must not move from page to page.
Questions, answered
What margins does my book need?
The outside, top and bottom must be at least 0.25 in — 0.375 in with bleed. The inside (gutter) margin depends on page count, because a thicker book curves more at the spine: 0.375 in up to 150 pages, rising in bands to 0.875 in beyond 700. This calculator gives you both the minimum and a recommendation that looks like a book rather than a document that met a requirement.
Why does the calculator recommend more than the minimum?
Because the minimum is a rejection threshold, not a design target. A book set at exactly 0.25 in outside has text almost touching the trim edge and under your thumb as you hold it. The recommendation adds a quarter of an inch to the gutter and lifts the outside to at least 0.5 in, which is roughly where published books sit.
What is a gutter margin?
The inside margin — the one at the fold. It has to be wider than the outside because part of it curves into the binding. On a left-hand page it is the right-hand margin and vice versa, which is what mirrored margins means.
What happens if I add pages after setting the margins?
If the new page count crosses a band boundary, the required gutter goes up and your compliant book quietly becomes non-compliant. This calculator warns when you are within 15 pages of a boundary, which is close enough that one revision could cross it.
Should the top and bottom margins be the same?
Traditionally the bottom is slightly deeper than the top, which makes the text block look optically centred rather than sitting low. Equal is fine. A top margin deeper than the bottom looks wrong to almost everyone, usually without their being able to say why.
Do these apply to IngramSpark too?
IngramSpark publishes its own minimums and they are not identical. This calculator implements Amazon KDP's published table. If you print through both, set margins to satisfy whichever is stricter for your page count rather than maintaining two interiors.
Have the margins checked against the real page count
Alhora knows your page count because it laid the book out, and re-checks the gutter when a revision pushes you into the next band.
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