Trim Size for Book Printing

Trim size is the final width and height of one book page after cutting. It does not include Bleed, crop marks, or the extra structural areas used for a cover.

A book listed as 170 × 240 mm will have finished interior pages measuring 170 mm wide and 240 mm high.

How Book Trim Size Is Written

Book sizes are written as:

Width × Height

A4 and A5 dimensions follow ISO 216. One inch is exactly equal to 25.4 mm, so inch-based book sizes can be converted directly into millimeters.

Use exact dimensions in the quotation and artwork. Names such as “A5 size,” “novel size,” or “standard book size” can be unclear when different markets use similar formats.

More standard dimensions are listed under Printing Product Sizes.

Trim Size Refers to One Page

For book interiors, the stated trim size refers to a single finished page.

For example:

• Single page: 170 × 240 mm

• Open two-page spread: approximately 340 × 240 mm

The spread width is useful while designing across facing pages, but the trim size remains 170 × 240 mm.

Set the Document at the Finished Size

Create the layout using the exact trim width and height. Keep any bleed outside the page boundary rather than adding it to the document size.

In Adobe InDesign:

1. Open File > Document Setup.

2. Choose a page-size preset or enter the exact Width and Height.

3. Select the correct orientation.

4. Review the layout before exporting.

Adobe identifies the InDesign page size as the document dimensions, while paper size refers to the larger physical sheet used for printing.

For an A5 book, the InDesign page remains 148 × 210 mm. The additional 3 mm area required for edge-to-edge artwork is handled through the document’s Bleed settings.

Confirm Trim Size Before Final Layout

Changing the page dimensions after the layout is complete can affect text flow, image crops, margins, and total page count.

InDesign includes an Adjust Layout function that can reposition or scale page elements after the width and height are changed, but the updated pages still need to be checked manually.

Confirm the trim size before finalizing:

• Interior pagination

• Full-page images

• Chapter layouts

• Page numbers

• Cover and spine dimensions

If the page count changes after resizing, the cover may also need an updated Book Cover Template.

Interior Trim Size and Cover Size

Interior trim size applies to one finished page. It is not the complete cover size.

A cover file includes the front cover, back cover, spine, and any structural allowances required by the binding method. Use the approved cover template rather than doubling the interior width manually.

Standard and Custom Trim Sizes

Standard sizes are useful when the project needs familiar proportions or must fit an existing shelf, carton, envelope, or mailing format.

Custom sizes are also possible. State the dimensions clearly, including the unit and orientation:

Finished size: 165 × 235 mm, portrait

Before confirming a custom format, check that it works with the selected paper, binding structure, and packing requirements.

Check the Exported PDF Size

Do not rely only on the original layout settings. Open the exported PDF and confirm its actual page dimensions.

In Adobe Acrobat Pro, Set Page Boxes can display and define the PDF’s trim, bleed, crop, art, and media boxes. The TrimBox should match the approved finished page size.

Check several pages when the document contains fold-outs, inserts, or other intentionally different page sizes.