# Gutter

> Source: https://www.infinitelibrary.ai/glossary/gutter

Last updated: 2026-09-06
Category: Typesetting & layout
Also called: Inner margin · Binding margin

The gutter is the inner margin where two facing pages meet at the spine; it is set wider than the outer margin because the binding swallows part of it.

## Definition

The **gutter** is the space at the inside edge of a page, next to the spine — technically the pair of inner margins on a spread, though the word is often used for the extra allowance added to them. It matters because a bound book does not open flat: in a **perfect-bound** paperback or a **casewrap** hardcover, some of the inner margin curves down into the binding and is lost to the eye.

The thicker the book, the more it loses, so gutter allowances scale with page count. A widely used schedule adds about **0.375 in** for books up to 150 pages, 0.5 in up to 300, 0.625 in up to 500, 0.75 in up to 700 and 0.875 in beyond that.

Too small a gutter makes readers crack the spine to see the text; too large a one wastes paper and pushes the text block outward. Lie-flat bindings such as coil sidestep the problem by opening fully.

## In Bindery

Bindery’s free watermarked proof shows the typeset spread at its real trim, so the gutter can be judged before printing; for books that must open flat, its coil-bound preset holds 2–470 pages.

## Related

- [Margins](https://www.infinitelibrary.ai/glossary/margins)
- [Spine width](https://www.infinitelibrary.ai/glossary/spine-width)
- [Perfect binding](https://www.infinitelibrary.ai/glossary/perfect-binding)
- [Lie-flat binding](https://www.infinitelibrary.ai/glossary/lie-flat-binding)
- [Trim size](https://www.infinitelibrary.ai/glossary/trim-size)
- [Photo Book Maker](https://www.infinitelibrary.ai/formats/photo-book-maker)
- [Lie-Flat Recipe Book Maker](https://www.infinitelibrary.ai/formats/lie-flat-recipe-book-maker)
- [Book Publishing Glossary — 59 Terms Defined](https://www.infinitelibrary.ai/glossary)
- [Bindery — the Claude-powered book studio](https://www.infinitelibrary.ai/bindery)

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