Bleed is artwork deliberately extended past the trim line so that when the printed sheet is cut, the ink runs right off the edge with no white sliver left behind. The standard allowance is one eighth of an inch, and it is needed only where something is meant to reach the edge of the page.
An interior of plain text needs no bleed at all. Bleed matters for full-page images, covers, and any element touching a page edge.
Why It Exists
Printing and trimming are separate operations, and trimming is not perfectly accurate. Stacks of paper shift slightly under the blade, so the cut lands a fraction away from where it was drawn.
If your image stops exactly at the trim line, a cut falling a hair outside it leaves a white edge. If the image continues past the line, the same inaccuracy simply removes a little more artwork and nobody notices. Bleed buys tolerance.
The same reasoning produces its counterpart, the safety margin. Because the cut can land slightly inside the line too, important content is kept back from the edge. Wiley asks that "all important type or images should be kept at least 6 mm (1/4 in) inside the trim of the book."
The Measurement, and Why Sources Differ
Every major printer specifies one eighth of an inch. The confusion is entirely in the metric conversion, and four different values are published:
| Source | Stated bleed |
|---|---|
| IngramSpark | 3 mm |
| Lulu | 3.175 mm |
| Amazon KDP | 3.2 mm |
| Wiley | 4 mm |
One eighth of an inch is exactly 3.175 mm. Lulu states the true value, KDP rounds up, IngramSpark rounds down, and Wiley is the most generous at "4 mm (1/8 in) past trim".
None of them is wrong in practice, because bleed is a tolerance rather than a target. Setting 3.175 mm satisfies all four. If you are working in millimetres and want one number, use 3.175 mm, or simply work in inches and set 0.125.
Which Edges Bleed
Three of the four. Wiley's wording is precise: elements "should extend 4 mm (1/8 in) past trim on head, thumb and foot", which is to say the top, the outer edge and the bottom.
The fourth edge, the spine side, does not bleed in a perfect-bound book. That edge is glued into the binding rather than trimmed, so there is nothing to trim off and nothing to guard against.
There is a real exception worth knowing, because it contradicts the flat version of this rule you will usually read. Wiley: "For mechanical bound books, elements should also bleed in the gutter." Spiral and wire binding punch through the page rather than gluing a spine, so that edge is trimmed and does need bleed.
Bleed Changes Your Page Size
This trips people up. A page with bleed is submitted larger than its finished size. A 6 by 9 inch book with an eighth of an inch of bleed on three edges is supplied as a canvas of roughly 6.125 by 9.25 inches, and the extra is cut away.
So a PDF that measures larger than your chosen trim size is not necessarily wrong. It may be correct and carrying its bleed.
Doing This in Deckle
Deckle applies bleed automatically for print PDF export, using a bleed size that defaults to 0.125 inches.
It applies bleed the way the printers describe it, extending the canvas on the top, bottom and outer edges while leaving the spine side alone, because that edge is bound rather than trimmed. The exported page is correspondingly larger than the trim size, which is expected.
You do not need to add bleed to a plain text interior yourself. Where it matters is full-page images, which must actually extend to the edge of the canvas rather than stopping at the trim line. An image that stops short leaves exactly the white edge that bleed exists to prevent.
Common Mistakes
- Adding bleed to a text-only interior. Nothing reaches the edge, so nothing needs it.
- Stopping the image at the trim line. That is the failure bleed prevents. Extend it past.
- Bleeding the spine edge of a perfect-bound book. That edge is glued, not cut.
- Treating an oversized PDF as an error. With bleed, larger than trim is correct.
- Putting text near the edge because bleed is on. Bleed protects artwork; the safety margin protects content, and Wiley asks for a quarter inch.
- Chasing the exact metric figure. It is a tolerance. 3.175 mm satisfies every printer.
FAQ
Q: Do I need bleed for a normal novel? A: No. A text interior has nothing reaching the page edge.
Q: Is it 3 mm or 3.175 mm? A: Both are the same eighth of an inch. Printers round it differently. 3.175 mm is exact.
Q: Why is my exported PDF bigger than my trim size? A: Because it includes bleed, which is trimmed off during finishing.
Q: Does the spine edge bleed? A: Not in a perfect-bound book. It does in spiral or wire binding, where that edge is trimmed too.
Q: What is the difference between bleed and margin? A: Bleed extends artwork outside the trim line. The margin keeps content inside it. They guard against the same inaccuracy from opposite directions.