To allow for deviations in cutting the paper to finished size an element that bleeds off the page is typically extended about 1/8" or 3mm beyond the trim lines. The amount of bleed allowance may vary depending on the method of printing and the press used.
Slight movement of the paper on the press or movement during cutting could result in items that are supposed to bleed off the edge not quite reaching the edge -- leaving a bit of paper showing at the edges. Bleed allowance extends the image off the page a sufficient amount to counteract these slight deviations.
Adding Bleed in Desktop Publishing Software
For software that doesn't explicitly provide for bleeds you can create a custom page size that is 1/8" (.125") larger on all sides. For example, instead of a 8.5" x 11" page, use a custom size of 8.75 x 11.25 then keep all content that doesn't bleed within the 8.5 x 11 design space minus the margins.- Adding Bleed to a Document in Adobe InDesign by David Blatner describes bleed guides and emphasizes the importance of your choices in the Marks and Bleed pane of the Print or Export PDF dialog box.
- Bleeds for Photoshop and InDesign has video tutorials.
- How to Create a Print PDF with Bleed gives instructions for InDesign and QuarkXPress, a workaround for Microsoft Word and Publisher.
- Bleed Guides is a video on setting bleed guides in QuarkXPress 8. No narration.
- Set Bleed Area Guides in PagePlus is from a tutorial on this site.
- Setting Up Crops and Bleed by Chris Spooner illustrates bleeds for Photoshop, Illustrator, and InDesign.
Elements that bleed off the page can sometimes add to the cost of printing if the printer must use a larger size of paper to accommodate the bleed allowance. To reduce costs, if possible redesign to eliminate the bleed or reduce the page size enough to fit the work on a smaller parent sheet of paper.
