I’m getting ready to redesign and rebuild the first A Moment of Clarity graphic novel, and I plan on working on a few new tools along the way to simplify the process for this book and for future ones. One of them will use Inkscape and Python to generate templates for perfect-bound book covers. If you’ve ever designed a cover for a perfect-bound book, you already know that one of the trickiest parts is calculating the width of the spine. There’s all sorts of calculators on the Web for doing this, but they’re usually geared toward the particular paper stocks that the printing company hosting the calculator has available. I want something more generic for this Inkscape plugin, something that can be used across printers as long as the right information is given.  This article is my attempt to glean as much of the knowledge about spine width calculations using English measurements that I can from the Web and distill it down into one guide.

A quick word of warning:  Keep in mind that I’m not a printer by trade — I’m just a simple comic book self-publisher — so if I’ve made a mistake, please let me know and I’ll correct it as soon as I can.  Also, talk with your printer before designing your cover to make sure that you have all of the right paper measurements for your print job.

Image by gregmote :: CC BY 2.0

How do I measure thee? Let me count the ways…

Some JavaScript spine width calculators on the Web use the average caliper size of the paper to perform their calculations. Other calculators use the Pages Per Inch (PPI) measurement for a specific type of paper. Most have some allowance for the thickness of the sheet of paper that constitutes your cover as well.  With the calculators I’ve seen, the measurements being used are buried in the JavaScript code.  Once you’ve read through all this, you should be able to make those calculations yourself, or at least understand how your printer is arriving at their measurements.

Ideally, you want to know the PPI of the paper stock you’ll be using.  Average caliper size or point size (which is the caliper size times 1000) are just as good.  Your printer should be able to tell you any of these measurements.  If not, you’ll have to guess.  Or find another printer. But hey, don’t let me tell you what to do. If you don’t know the PPI, caliper, or point size of the paper your printer is using, but do know the type of paper and its weight, you can estimate PPI or caliper using the charts on the Case Paper or the Micro Format site.

For instance, let’s say your printer uses 20# bond paper, a pretty standard paper weight, to print the interior pages of your 200 page book. Most likely, the caliper size of this paper is .004, but again, verify this with your printer before proceeding. Calculate the PPI by diving the number 2 by the caliper size:

2/.004 = 500

The PPI of this paper is 500, which means that, for every 500 pages in your book, the spine will be 1 inch thick.

Now, with the PPI, you can calculate the thickness of the spine, without the allowance for the cover. The size of the spine for the interior pages will be:

200/500 = .4 inches

Next, do the same for the cover. Let’s say your cover is going to be printed on 9pt paper stock. Points to caliper is a really easy conversion — divide the points by 1000 to get .009, then calculate:

2/.009 = 222

Since the cover is four “pages” (outside and inside covers), the additional inches you need to add to the spine will be:

4/222 = .018

So your final spine width in inches for a 200 page book printed on 20# bond with a cover that is printed on 9pt stock is:

(200 / (2/.004)) + (4 / (2/.009)) = .418

.4 + .018 = .418 inches

All this, of course, is different in metric. I’ve only dealt with printers who work in English measurements, and haven’t been able to find a lot of info on metric measurements for perfect binding books. If you know of any sites that deal with calculating the spine width for perfect-bound books in metric, please leave a comment and I’ll update the article. So far, I’ve found this one: Allander Print Unlimited.

For a good rant on how crazy all of these different measurements seem, read Brian Cowie’s post at The Paper Mill Store called Paper Weights Demystified in Five Minutes. Also, get more nitty-gritty details at Wikipedia in the Paper Density article.  And, expect to see more info on the Inkscape Perfect-Bound Cover template generator in the next few days.

This entry was posted on Saturday, October 20th, 2007 at 9:48 pm and is filed under A Moment of Clarity. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.