This is one of the most common questions we answer at PrintHouse.
Bleed is a specific area (usually 3mm) added to each outside edge of a page as an aid for the finisher to be able to trim the final document correctly.
For example, a document at A4 size, being 210mm x 297mm will measure 216mm x 303mm with 3mm bleed added to each of its 4 edges, giving a document size that is 6mm bigger in both height and width. This is said to be an A4 document with bleed. The same applies to any page size and will always require 3mm bleed as standard to each of the edges original dimensions.
So why do we need to add bleed?
It helps to have an understanding of the finishing process in order to answer this. The document will be printed on a larger sized paper than the original page size, often with a few copies of the same page to print as many as possible at once. This will depend on the press size. After the document has been printed, it will be trimmed on a large guillotine. The paper will be stacked high and a blade will pass through the stack, cutting away the unwanted paper.
Imagine a document with a solid colour background for example. The blade has to trim exactly along the edge of this colour on each page in the stack. What will happen if some of the pages have moved slightly whilst in the press or on the guillotine and the crop marks do not register properly? The blade will trim some accurately, but those pages that have moved may have a slight strip of white paper with no print on the edge. It looks very bad and quite unprofessional. Therefore, a solution is needed for the inevitable movement of each sheet when printing and finishing.
So, is adding bleed just a case of putting a 3mm white border around the edge?
No. Definitely not. Thinking about the problem above, this would not solve the issue of the blade having to hit each edge completely accurately. Therefore, what bleed does is continue the print over the edge so that the guillotine has something to trim into. For example, the A4 sheet I mentioned earlier with a solid background…this would need the colour extending over the edge of the A4 page and into the 3mm on each edge. This way, the guillotine has 3mm of colour on each outside edge to trim into allowing for any movement but still giving a finished trimmed size of A4 with no white/paper edges. Solid colour will run to the edge of the page.
What happens if I have elements or pictures that I need to bleed?
That’s fine. Exactly the same principle applies. Each element that needs to touch the edge of the paper when trimmed will need to extend 3mm over the edge of the finished page size. This is easily done in most cases, especially for solid fills. However, pictures can sometimes be a problem. For example, you may have a picture that is A4 in size and want it trimmed to the edges. Unfortunately, the only way of doing this is extending the picture 3mm over each edge and then losing this area outside the page size when it is trimmed. Pick your pictures wisely! Choose pictures that have parts you do not mind trimming into. The same goes for any other elements. Bleed will always need to be considered as part of the design composition.
The black box and trim marks show the final business card size after trimming. Notice how the picture in the top left overlaps the trim marks. This is called the bleed area. The overlapping part of the picture will be trimmed away when the cards are finally cut.
Hopefully, this will give you some idea on how bleed is set up and why it is needed in design and print.
Don’t hesitate to contact us here at PrintHouse to discuss your design or print projects. You can call on 020 8963 0123 or just go ahead and use the contact form below. We’ll get back to you to discuss your printing project.