Fold Lines for Book Printing

Fold lines show where a flat printed piece will be folded. They are used for folded inserts, gatefold pages, dust jackets, covers, flaps, and other continuous components.

A fold line is only a layout and production reference. It is different from a trim line and should not appear on the finished product.

Place Fold Lines from the Flat Artwork Edge

Fold positions are measured across the full Flat Size, not from the size of the folded panel.

For a simple half-fold insert measuring 200 × 210 mm, the vertical fold line sits at:

100 mm from the left edge

For multi-panel pieces, calculate each position from the actual panel widths:

Do not divide the artwork into equal panels unless the confirmed structure uses equal panels. Roll folds and wrapped panels often need a slightly narrower fold-in panel so the finished piece closes properly. The production template should take priority over a manual calculation.

Keep Important Content Away from the Fold

Avoid placing small text, logos, barcodes, faces, or thin borders directly on a fold line. Paper can shift slightly during folding, and the fold itself can interrupt fine details.

As a practical starting point, keep important content at least 3–5 mm away from each side of the fold. More clearance may be needed for thick paper, scoring, or complex folding structures.

Background colors and large images can cross a fold, but check that the design still looks correct after the panels are closed.

Inside and Outside Artwork

A double-sided folded piece normally needs two pages:

• Page 1: Outside

• Page 2: Inside

Both pages must use the same flat dimensions and the same fold-line positions.

The panel order will look different on the outside and inside, so do not copy the artwork from one side and simply mirror it. Check which panel becomes the front, back, flap, or inside section after folding.

Fold Lines and Score Lines

A fold line marks the intended position in the artwork. A score or crease is the physical indentation added during production to help the paper fold cleanly.

The artwork usually shows only the position. The production specification confirms whether the sheet will be folded directly or scored first.

How to Supply Fold Lines

Use non-printing guides while designing. Do not draw permanent dashed lines across the artwork unless they are specifically requested.

When visible fold indicators are needed, place them on a separate named layer or provide a reference PDF. The final production PDF should normally remain clean, without fold lines running through the printed design. Some commercial-printing workflows show fold indicators only on the proof rather than the press-ready file.

Set Fold Lines in Adobe InDesign

1. Turn on View > Show Rulers.

2. Drag a ruler guide onto the page.

3. Select the guide and enter its exact X or Y position in the Control panel.

4. Add the remaining guides according to the panel measurements.

5. Lock the guides before adjusting the artwork.

Use page guides for one page or spread guides when the same line must continue across a spread. InDesign ruler guides are layout references and can be positioned using exact coordinates.

Keep the document at the confirmed flat dimensions, add Bleed around the outer trimmed edges, and make sure the fold positions match on both the inside and outside files.