I asked for something I thought was simple. When you print a book, the spine and the back cover are one image with the front, so the app should let a writer add a picture, put text into a template, and get one file. I asked why this was not standardised, and how printers could be using different bleeds.
That question had a better answer than I expected, and I got part of it wrong.
01What I assumed, and the correction
I had assumed the paperback bleed measurements would differ. The specifications in my notes agreed. Bleed is the extra picture that runs past the cut edge so no white shows when the page is trimmed. The paperback specifications in my notes all use 0.125 inches of it, and an earlier draft of my own notes that said otherwise was wrong and has been corrected.
Three things still differ.
02The spine is a measurement of an object
A spine is the page count divided by the stock's pages per inch, and that figure belongs to the actual paper on the actual press. Amazon's white stock runs at 444 pages per inch. Another printer's uncoated 50lb paper comes from a different mill and is a different thickness.
On the same 276-page novel, the answer from Kindle Direct Publishing is a 0.622 inch spine and my estimate for IngramSpark is 0.636. That is 0.014 of an inch, which means nothing until it is the difference between a title sitting in the middle of a spine and creeping round the fold.
The 444 and the 0.622 come from Kindle Direct Publishing's own documentation. IngramSpark does not publish its stock figure anywhere I could check, so the 0.636 is an estimate from the usual trade figures, and the app marks it as an estimate and tells the writer to download the real template before sending files. Two of the calculator sites I tried disagreed with each other.
03A hardcover is a different object
A paperback folds around the block of pages. A hardcover case wraps boards, so it needs a turn-in and the board's own thickness. IngramSpark asks for 0.625 inches of bleed on a case, against 0.125 on a paperback. For that same 276-page novel at 6 by 9 inches, the full cover comes to 12.89 by 9.25 inches as a paperback and 14.14 by 10.25 as a cased book.
04House rules
Each printer sets its own minimum for spine text. Kindle Direct Publishing will not letter a spine under 79 pages.
05So there is no one template
The cover editor uses the measurements of the printer you pick, and says which. That is more honest than a single rectangle that is wrong for everyone a little.
This is the cover work I was doing in September. The next post is about what happened when I asked a second reader to find what would go wrong at the printer.
Thanks for reading.
J.H.
How this post was made
Taken from COVER_WRAP_2026-09-17.md in the Mac app's deliverables folder. The printer figures come from the printers' own documentation as recorded there, as they stood in September. Drafted by Grok Bot and GPT-6 Astra on behalf of Jamie Heerlyn.