Ebook covers are a picture. Print covers are a manufacturing specification, and the difference catches out everyone who does the second one after doing the first.
You are not designing a front cover. You are designing a single flat sheet that gets printed, wrapped around a stack of paper, glued at the spine, and then trimmed on three sides by a machine with a tolerance of a couple of millimetres.
The three parts of one image
Laid out left to right, a paperback cover file is: back cover, spine, front cover. That order is not arbitrary — it is the order the sheet wraps.
| Region | Width | Contains |
|---|---|---|
| Bleed | 3mm on each outer edge | Background only — it gets cut off |
| Back cover | Trim width | Blurb, author note, barcode area, price |
| Spine | Page count x paper thickness | Title, author, publisher mark |
| Front cover | Trim width | Title, subtitle, author |
So a 6 x 9 inch book with a 12mm spine produces a cover file of 2 x 152.4mm plus 12mm, plus 3mm of bleed on the left and right — 322.8mm wide — by 228.6mm plus 3mm top and bottom, or 234.6mm tall. Those numbers are the whole job. Get them wrong and the printer either rejects the file or prints a book with the title creeping around the front edge.
Calculating the spine
Spine width is page count times paper thickness. The page count is the number of *pages*, not sheets — a 200-page book has 100 sheets, and you multiply by 200.
spine (mm) = page count x per-page thickness
White paper 0.0572 mm per page
Cream paper 0.0596 mm per page
300 pages, cream: 300 x 0.0596 = 17.88 mm
120 pages, white: 120 x 0.0572 = 6.86 mm- Use your printer's own figure. The numbers above are Amazon KDP's for its standard stocks; another printer, or a heavier paper, gives a different result. They all publish theirs.
- Round nothing yourself. Most services provide a template generator that takes trim size, page count and paper colour and hands back an exact file. Use it.
- Below about 100 pages there is no spine to print on. Most services will not accept spine text under roughly 130 pages, because the tolerance is wider than the spine.
- A page count that changes changes the cover. This is the whole trap, and it deserves its own section.
Why the interior has to be finished first
Adding a paragraph to chapter two can push the book from 246 pages to 248, which changes the spine by a tenth of a millimetre, which shifts every element in the cover file sideways. Do this three times and you have rebuilt the cover three times.
The correct order is: finish the manuscript, typeset it, export the final interior PDF, read the page count off that file, and only then build the cover. Estimating pages from a word count is fine for planning the spine roughly; it is not a number to design against.
- Freeze the interior. No more edits, including typo fixes, until the cover is built.
- Export and check the page count in the actual PDF, including front matter, blank pages and the notes at the back.
- Round up to an even number. A book has an even page count; the printer will add a blank if you do not.
- Generate the template with that number, and build the cover inside it.
- If the interior changes afterwards, regenerate. Do not nudge the artwork by eye.
The safe zone, and what goes wrong in it
Trimming is accurate to within about 2mm, and the whole cover can shift slightly as it wraps. So there are two boundaries: the trim line, where the paper is meant to be cut, and a safe zone about 5mm inside it, where anything you actually want to keep must live.
| Mistake | What the printed book looks like |
|---|---|
| Title 3mm from the trim edge | Title touching the edge, or half a letter missing |
| No bleed on a background image | A thin white line down one side |
| Spine text centred on a 6mm spine | Text creeping onto the front and back |
| Barcode area covered by artwork | Rejected at upload |
| A border framing the whole cover | A border of visibly uneven width |
The last row is the one that surprises designers. A thin frame around the edge of a cover is the single least forgiving thing you can put on one: a 1.5mm trim shift is invisible on a photograph and glaring on a border, because the reader has four parallel lines to compare against each other.
What the back cover has to carry
The front sells the book to someone across a room. The back sells it to someone holding it, and it has a fixed set of jobs.
- The blurb — 100 to 150 words, present tense, ending on a question rather than a summary.
- A line about the author, two sentences at most, and only what makes them the right person to have written this.
- Clear space for the barcode, usually about 51 x 31mm at the bottom right. The printer places the ISBN barcode there; artwork underneath it will be covered or rejected.
- The publisher mark and category, if you have them. A single word — "Fiction", "Memoir" — helps a bookshop shelve it.
Keep the type consistent with the interior. A cover set in a face that appears nowhere inside reads as two projects stapled together, which is the same discipline that keeps a series looking like a series. And whatever else you do to the cover, the interior it wraps should be genuinely print-ready before you spend an evening on the spine of a book that is not finished.