How much bleed do I need for printing?
Short answer
Bleed is artwork extended beyond the trim line so that cutting variance does not leave an unprinted edge. Typical requirements are 3 mm for digital and commercial print, and 10 mm or more for large format where finishing needs extra material.
Why it exists
Cutting is mechanically accurate to a tolerance, not absolutely. If artwork stops exactly at the trim line, a variance of a fraction of a millimetre shows the substrate. Extending the artwork past the trim means the cut always falls inside printed area. The same logic applies to contour cutting, where the tolerance is often larger.
Trim size 100 × 150 mm Bleed 3 mm all round Document 106 × 156 mm Safe margin 4 mm inside trim
When bleed can be added afterwards
When the artwork already continues to the trim edge, the existing content can be extended outward, or the edge can be mirrored, without changing the design. This is safe and can be automated. It is the most common single repair in prepress.
When it cannot
If the design ends at the trim — a white border, a photograph that stops, text close to the edge — there is nothing to extend. Inventing content would change the design. The correct answer is to report the problem and ask for a file built with bleed, or agree to a visible margin instead.
How Prepta handles it
Prepta generates bleed to the amount your profile requires where the surrounding content makes it safe, following the contour on die-cut work rather than a bounding box. Where the artwork does not continue to the trim, it reports the missing bleed with the affected edges instead of fabricating them.