Book | Spine Width Calc | Number of Pages vs. Number of Sheets?

[Joe-New-to-ID]

I'm creating a cover-spine-back cover file now in Adobe InDesign for my book. We all know that the spine width is dependent on the number of "pages". A general formula is as follows:

• Spine Width = (Number of Pages) x (Thickness/Page)

What is really meant here: the number of pages (112 in my case) or the number of sheets (physical pieces of paper; 66 in my case)? I believe it is the latter, but I find nothing clarifying this matter via Internet searching conducted so far (e.g., KDP set up), and I want to make sure I'm not missing something.

[Mike Witherell]

It would be pages stacked up. Sheets that are folded 2-up, would be half that number, for example, even as you noted. Your question reminds me how much variation in terminology there is in the printing industry, even within one country. Page numbers would occur 2 on each page/sheet: one on the front and one on the back of each page/sheet of a printed book. 

[Joe-New-to-ID]

Mike:

Thank you. I think that what you are saying is that with my core book being 112 pages as counted via InDesign's page layouts, the number to use in the spine width formula is 66 sheets. That is, what matters is the number of physical sheets as if they were unfolded and stacked one on top of the other. For example, if I had a 10-page book (unrealistically thin, but used here for illustration), my sheet count to use for the spine width calculation would be as follows:

Pages 1-2 = 1 Sheet

Pages 3-4 = 1 Sheet

Pages 5-6 = 1 Sheet

Pages 7-8 = 1 Sheet

Pages 9-10 = 1 Sheet

Total = 5 Sheets

Spine Width = (5 Sheets) x (0.002252 Inches/Sheet) = 0.01126 Inches

Is this correct?

[Mike Witherell]

yes! and as others have discussed, it is even more accurate if you get the info from the commercial printer doing the job.

[Joe-New-to-ID]

Mike:

Thank you. I will proceed accordingly.

[rob day]

You should get the spine bulk from the printer.

[Joe-New-to-ID]

Rob:

Thank you for the response. What is a spine bulk? The spine width? Are you saying that I should not use a rule-of-thumb formula but to consult with a book printer to get a bona fide spine width up front?

[rob day]

Yes.

For example this printer’s bulk calculator returns a different width depending on the sheet:

https://colorhousegraphics.com/spine-bulk-calculator/

[Joe-New-to-ID]

Rob:

Thank you!

[James Gifford—NitroPress]

The thickness will depend on the EXACT paper being used and the printing/binding processes used by that printer. So even if you have a spec for the same paper, from a mill or another printer, it may not be accurate.

YOUR printer should either give you a value or point you to a setup page with a specific calculation.

[Joe-New-to-ID]

James:

Thank you.

[James Gifford—NitroPress · Accepted solution]

Most formulas from book printing services are asking for the number of print pages, which of course would be nominally half that number of sheets.

Amazon/KDP, for example, gives the value of 0.002244 for the thickness of a page... which is actually half the thickness of each sheet or "page" in the book.

 A quick calculation will usually show if you're wrong — in most cases, it's evident that the thickness calculated is either half or double what it should be. Compare the figure with other books at hand of similar size as a rule-of-thumb check.

But "page" usually means each printed page, not sheets (2 pages), which would have to be a separate calculation that might get screwed up. 🙂

[Joe-New-to-ID]

James: Thank you very much!