Flat Size for Book Printing

Flat size is the full width and height of a printed piece before it is folded or assembled.

It is mainly used for folded inserts, gatefold pages, dust jackets, book covers, and other components made from one continuous sheet. A normal interior page without folds is usually described by its Trim Size instead.

Flat Size and Finished Size

Flat size and finished size describe two different stages:

Bleed is not included in the stated flat size. It extends outside the flat-size boundary in the artwork file.

How to Calculate Flat Size

For a simple half-fold piece:

Flat width = Finished panel width × 2

For example, an insert that finishes at 100 × 210 mm after one vertical fold has a basic flat size of:

200 × 210 mm

With 3 mm Bleed on every outer edge, the exported artwork area becomes:

206 × 216 mm

The flat size remains 200 × 210 mm. Bleed does not change the stated product size.

Multi-Panel Pieces

For a piece with several panels, add the actual width of every panel:

Flat width = Panel 1 + Panel 2 + Panel 3 + …

Do not assume that all panels are equal. Roll folds, gatefolds, and some wrapped structures may require narrower inner panels so the piece can close properly.

The approved template should already include this folding compensation. Place artwork according to the supplied Fold Lines rather than dividing the total width evenly yourself.

Flat Size for Book Covers and Jackets

A complete softcover layout includes:

Back cover + Spine + Front cover

A dust jacket may also include front and back flaps. Its flat width is therefore:

Back flap + Back cover + Spine + Front cover + Front flap

Hardcover layouts can include board widths, joints, spine areas, and turn-ins. These measurements depend on the final page count, materials, and binding structure, so use the approved Book Cover Template instead of calculating the file from the finished book width alone.

Set Up the Artwork

Create the document page or artboard at the exact flat size. Add bleed separately around the outer edges.

For a double-sided folded component:

• Page 1 contains the outside artwork.

• Page 2 contains the inside artwork.

• Both pages use the same flat dimensions.

• Fold positions must align on both sides.

Folded print files are normally prepared at their full pre-fold dimensions rather than as separate finished panels.