How big should my book’s gutter be?
The gutter is the inside margin of each page, next to the spine. When a book is open, the pages curve into the binding, so text placed too close to the spine is hard to read — or disappears completely. The thicker the book, the bigger the curve and the wider the gutter needs to be. This gutter margin calculator gives you the right inside margin for your page count and binding.
Gutter by page count (KDP)
| Pages | Minimum inside margin |
|---|---|
| 24–150 | 0.375 in |
| 151–300 | 0.5 in |
| 301–500 | 0.625 in |
| 501–700 | 0.75 in |
| 701–828 | 0.875 in |
KDP hardcovers (75–550 pages) use the same table.
Other bindings
- Saddle-stitched booklets (stapled, up to about 64 pages) open almost flat, so about 0.25 in is usually enough.
- Spiral, wire-O and coil bindings need room for the punched holes — about 0.625 in is a common starting point.
- Always check your printer’s own specifications for these bindings.
Gutter vs Word’s “gutter” setting
In Microsoft Word, the simplest method is mirror margins with the full inside value in the “Inside” box and the separate “Gutter” box set to 0. Our Word template is already set up this way.
See all four margins with the book margin calculator, and the full page size with bleed in the book bleed calculator.
What the gutter is
The gutter is the inside margin — the edge of the page closest to the spine. A paperback does not open flat, and the thicker the book, the more of each page curves into the binding. A wide enough gutter keeps your words out of that curve.
KDP gutter by page count
| Pages | Minimum gutter |
|---|---|
| 24 – 150 | 0.375 in (9.6 mm) |
| 151 – 300 | 0.5 in (12.7 mm) |
| 301 – 500 | 0.625 in (15.9 mm) |
| 501 – 700 | 0.75 in (19.1 mm) |
| 701 – 828 | 0.875 in (22.3 mm) |
Example
A 250-page 6 × 9 in book needs at least a 0.5 in gutter. If edits push it to 310 pages, the minimum jumps to 0.625 in — and a PDF made with 0.5 in would be rejected. Enter your page count and binding to get the right value, then add a little extra for comfort.
Check your text fits
Enter your font size, line spacing and word count to see how a bigger gutter changes the page count. A larger gutter makes the text block narrower, so the book gets a few pages longer.
Common gutter mistakes
- Counting the gutter twice — in Word, set it in “Inside” with mirror margins and leave the separate gutter box at 0.
- Not updating it after edits that change the page band.
- Using the same margins for hardcover and paperback without checking both.
Set all four margins at once with the book margin calculator.