Though printed as a flat sheet, a paperback cover becomes a three dimensional object when it’s bound to the book. While digital and offset presses print with extreme positional accuracy on the order of 1/1,000″, binding and trimming machines typically have tolerances of plus-or-minus 1/16″. What looks spiffy on a screen may not work by the time a book goes through all the steps in printing and binding. This post is about laying out your cover files in InDesign or Quark so that you get the result you want on your finished paperback books. It is not a post about color theory or design or typography, just nuts and bolts book geometry. I’ll cover dust jackets and endsheets in a future post.

Parts of a Paperback Cover

How Close to the Edge?
Wrapping Images
Checklist for Sizing a Paperback Cover


In book databases, conflicting terms are used to denote the dimensions of a book. In one database, for example, the term for the distance from the top of the front cover to the bottom is “height”; in another the same measurement is “depth.” Here’s the terminology we use, which is based on printers’ customary practice:

  • If the book is standing up with the front facing you, width is the horizontal dimension from spine to foreedge, and height is the vertical dimension from top to bottom. The top of the book is the head, the bottom is the tail.
  • Now turn the book so the spine faces you. Spine width is the horizontal dimension of the spine. This is, obviously, the same as the distance from the surface of the front cover to the surface of the back cover, i.e., the thickness of the book.

I’m going to show you how to come up with the measurements for your paperback covers yourself. However, here’s an up-front recommendation: have your printer provide a template showing you the exact dimensions of your cover. (At Bookmobile, contact your customer service representative, and also note that spine widths are provided in our estimates.) That way, it is up to the printer to make any tricky calculations, and check with you if anything is off with your cover file. As long as you provide a file exactly matching the dimensions specified on the template, it is their responsibility to print and bind the cover correctly. Any real book printer can provide a cover template. Templates are based on the exact text paper, cover material, and page count you specified when you requested a quote or ordered the job; if either one changes for any reason, you will need a new template from the printer. Also, be sure to include roman-numeraled frontmatter pages and any blanks in your page count total: they all count when you’re printing and binding!

Parts of a Paperback Cover

Paperback covers have five parts:

  • Front cover
  • Spine
  • Back cover
  • Bleed

The Front Cover

The front cover is what you see when you are looking at the front of the book. On a finished book, it is exactly the same size as the pages in the book. That is, on a paperback whose pages are 6″ x 9″, the front cover will be 6″ wide and 9″ in height. Double check this! You would be surprised at how often we get a cover file laid out for one page size, while the file for the interior of the book is laid out at a different one. When the razor-sharp blades of that old three-knife trimmer come slicing down, they’d better be identical, or you’re going to have a big problem either with the cover or the pages. FYI, at Bookmobile, our interior and cover preflight departments work together to make sure trim sizes are accurate.

The Spine

The spine is the area of the book cover to which the pages are glued on the inside. On a finished book it is exactly the same height as the pages in the book; for example, on a book with 6″ x 9″ pages, the spine height is nine inches. The spine width is more complicated, as it depends on the number of pages in the book, the pages-per-inch (PPI) of the paper the pages are printed on, and the thickness of the cover material. The formula is:

Spine width in inches = (Number of pages / PPI) + allowance for cover material

For example, if a book has 600 pages, the text paper is 400 PPI, and the allowance for the cover is .015625”, the spine width is calculated as follows:

1.515625″ = (600 / 400) + .015625

1.515625 decimal inches ≈ 1-17/32 fractional inches

It is critical to get the spine width as close as possible to the actual width of the book. Because humidity and different manufacturing batches affect the actual PPI of the paper, whatever the nominal PPI, the printer should double-check the spine width and fine tune as necessary. We do.

If you have the edge of a color panel or other graphic running along the turn of the spine from the front cover and/or the back cover, an inaccurate spine width will force the binder operator to choose the lesser of evils because it will be impossible to match up the spine to the book block perfectly. The operator can only 1) align one edge where the spine meets the front cover or where it meets the back cover, or 2) center the spine over the back of the book block, which will result in the spine showing on the front and back cover if the spine is too wide, or the edges of the front and back cover showing on the spine if the spine is too narrow.

The Back Cover

The back cover is exactly the same size as the front cover and therefore exactly the same size as the book pages.

The Bleed

Absent in the final book is the bleed, which is removed in the final trimming of the head, foreedge, and tail of the bound book. You may ask, if it is going to be trimmed off, why is it there in the first place? Why not just print the cover to the edge of the finished pages, bind it all up and be done with it? Well, remember what I said about binding equipment being accurate only plus-or-minus 1/16″? Neither the cover nor the text pages would be trimmed to exactly the right size if trimmed separately. Allowing the extra amount (the bleed) both all around the cover and on the book pages enables them to be trimmed after they are bound to precisely the same dimensions.

The other key benefit of bleeds is that if an image is supposed to visually run off the edge of the cover—or the edge of an interior page, for that matter—if we extend the image into the bleed area we can be confident that when the book is trimmed we will not accidentally have an unsightly, probably crooked, white line along the edge. Without extending the area of the color or image into the bleed we would stand about a 50 percent chance of having such a blemish.

Sometimes the image, when sized just right, doesn’t extend into the bleed. The solution is to clone a strip of the image along the edge, flip the clone so that it is a mirror image of the edge of the main part of the image, and nudge it over into the bleed, butting the clone up perfectly to the edge of the main part of the image. Any imprecision in trimming will be completely invisible. However, if there is an identifiable object at the edge of the cover–the top of a head, for example–a mirror-image clone can create peculiar artifacts. In such cases more extensive image retouching will be called for.

The normal width of a bleed is 1/8″. Be sure to check “include bleeds” when you create the PDF file!

Asking for Trouble: Running Critical Cover Elements to the Edge of the Paperback Cover

Because the binding process has fairly large tolerances, and because the human eye has an amazing ability to detect non-parallel lines, running a straight-line design element parallel to any edge of a cover within about 1/4″ of the edge is dangerous. The eye will instantly detect the converging lines. A frame on the front, spine, or back is even worse, as each edge of the rectangle will likely appear askew unless, by random chance, the frame was both centered and its edges square with the trimmed edge of the book—which is unlikely to happen.

Asking for Trouble: Wrapping an Image Around the Front Cover, Spine, and Back Cover

When a cover is laid out in InDesign and the designer is handed a horizontal image to use, there is the temptation to lay out the image all the way across the whole cover from back on the left, across the spine, and across the front cover on the right. This might look cool on the screen, and on the printed covers before they are bound, but it is a dead end once the book is bound: the person viewing the book can only see two surfaces at most—front and spine, or back and spine—unless they are living in the same universe as Les Demoiselles d’Avignon. Plus—and this is based on personal experience—the areas of the image suitable for laying type over always seem to be wrong place. That said, of course, there is no design rule that shouldn’t be broken under the right circumstances.

Checklist for Paperback Cover File Prep

  • Make sure the front cover and back cover are exactly the same size as pages of the book.
  • Allow 1/8″ bleed around the entire edge of the flat cover: run any color areas or images into the bleed area.
  • Avoid straight-line graphic elements parallel to the trim edge and within 1/4″. Ditto frames within the front cover, spine, or back cover.
  • Request a cover template from your printer and follow it exactly.

For more about file prep, see my post Why We Have to Do Prep Work on “Print-ready” Files.

Need a quote or more information?

I’d be happy to answer questions. Contact me via email.
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