Book margins: how to set mirror margins, gutter and safe areas
Book margins aren’t a fixed number—they evolve as you write and as specs change. Page count and the paper stock you’ll print on both affect the ideal margins. The purpose of margins is to keep the text comfortably centred on the bound page. Always account for the binding edge (the gutter), especially with perfect bound and hardcover books.
Margins should not be used to force where text ends on a page or where a chapter breaks. It’s tempting to “nudge” margins to make content fit—don’t do this. Set margins for readability and binding, not pagination tricks.
Word document setup
As a general rule, start with 20 mm on all sides and add an additional gutter for the binding edge. In Microsoft Word, set the document up with the following:
- Mirror Margins for the whole document — this creates separate inside/outside margins for facing pages.
- Binding Edge (Gutter) — either increase the inside margin manually, or use Word’s dedicated Gutter setting (recommended).
- For this guide we’ll use the Gutter option so Word adds the extra space on the binding edge automatically.
Tip: In Word go to Layout → Margins → Custom Margins…, choose Multiple pages: Mirror margins, then set Gutter and Gutter position: Left.
Worked example (your specs)
Trim size: 152 mm × 229 mm | Page count: 200 pages | Stock: 100 gsm uncoated
Before calculation
| Side | Margin |
|---|---|
| Top | 25 mm |
| Bottom | 20 mm |
| Inside | 20 mm |
| Outside | 20 mm |
After calculation (with these specs)
| Side | Margin |
|---|---|
| Top | 25 mm |
| Bottom | 20 mm |
| Inside | 20 mm + 6.25 mm gutter |
| Outside | 20 mm |
The extra 6.25 mm accounts for binding “swallow” so inner text doesn’t crowd the spine. Exact gutter depends on paper thickness and page count.
Get exact measurements
For precise inner/gutter values based on your actual page count and paper stock, use our Book Margins Calculator, then update Word’s Mirror margins and Gutter accordingly.