The traditional way of constructing a hardcover binding used to be as follows: First you had to bind the book block and then take the measurements – these are the width, height and bulk (thickness). Then the binders cut the boards, the inlay or spinestrip, and the covering materials. A library binder, binding or rebinding one book at a time, usually had no other choice but to follow this rule. There are just too many variables for each book to be bound. They have to take much into consideration—trim or no trim; grinding or not grindingoff the spine; thickness of the bookblock; and type of the hardcover binding (rounded and backed, flatback, endpaper structure). They all influence the critical measurements required for making a beautifully fitting hardcover case.
Manufactured papers have a caliper. The caliper of the paper is the measured thickness of a single sheet by the use of a micrometer when a specified static load is applied for a minimum specified time. Since papers vary in their thickness and are compressible, the bulking number is measured in a manner that predicts the bulk of a book under the conditions of production. Paper companies and suppliers provide this data, expressed in pages per inch or PPI. For example if they list a certain paper to have 500 PPI, it means 500 pages will make a bookblock that is exactly one inch thick. Now watch out and be aware that a sheet has two pages! In other words, 250 sheets of a 500 PPI paper will equal one inch. Let’s take a few examples and discuss the dimensions needed for hardcover cases.
Flat or Square hardcover cases are much different from rounded and backed ones. If the book block is adhesive bound and the endpaper flexes at the binding edge, such a cover structure is different from a binding that is sidesewn. If oversew endsheets are used, treat it like one that flexes at the very binding edge.
For an example, let us assume that our bookblocks have a trim size of 6 x 9 in and a bulk of approx. 3/8". An average, median board is used (0.080"). The calculations of board, spine (inlay) and cover dimensions for a square back hardcover flexing at the binding edge is calculated as follows:
Board Sizes 

Trim size  6"  x  9" 
Hinge area  Less ¼"  
Extensions  plus 1/8"  plus ¼"  
Board size 
5 7/8" 
x 
9 ¼" 
Width of Inlay Strip 

Board thickness  0.080"  
Spine thickness  plus 3/8"  
Board thickness  plus 0.080"  
Width of inlay strip 
½" 
That is the width of the spine strip. Therefore, cut the spine strips ½ x 9¼". This should be done on a board shear. If the strips are cut on a guillotine cutter, one of the edges of the strip is slanted, often resulting in a poor quality, distorted spine.
Board sizes for square back book
Now we are ready to calculate the dimensions of the cover and covering material.
If the spine strip has a width of ½", add 3/8" on each side. The 3/8" gaps represent the joint areas. Bear in mind when using thicker boards, you must add a little more to this area, as the covering material has to go over the spine strip. An insufficient joint area may result into unusual stress exerted onto the first and last pages of a binding.
Cover dimensions for square back hardcover
Cover Size = Board Size + between the boards + board size
Cover Stock = Cover Size + Turn in allowance
Cover dimensions 

Board size  57/8"  X  91/4" 
Joint area Inlay strip Joint area + Between the boards 
3/8" plus ½" plus 3/8" equals 1¼" 

+ Board size  57/8"  
= Cover size  13"  x  91/4" 
+ Turnins (all four sides) 
5/8" plus 5/8" 
5/8" plus 5/8" 

Cover stock dimensions 
14 ¼" 
x 
< 10 ½" 
Sidesewn book blocks with Singerstyle endsheets require different calculations because the cover board must flex further inward.
Now let us look at, how we can calculate the cover dimensions for hardcover books that are rounded or rounded and backed.
Rounded and Backed book blocks are more difficult to calculate. The bindings always required making sample books—a labour intensive and expensive task. There is a mathematical solution to figure out the exact cover dimensions, even if the paper is not yet available. All we need from the publisher’s production managers are the trimsize, the type of paper used, the number of pages (and the PPI), and the style of hardcover binding. We are almost ready to calculate. But now you ask, how in the world can you determine the distance over the rounded and backed spine? After all, the width of the flexible inlay is a most important item to achieve a quality hardcover binding. Well, there is a trick to it. You must establish a chart. In my case, during a slow period, I bound 20+ Smythsewn book blocks. They all had the same trim size. The only variations were the bulk. I started with a ¼ inch thick book, the next having a 3/8 inch bulk – all the way up to 3 inches. Then I rounded and backed the book blocks the way they should look like in production. That required some craftsmanship. When I had all book blocks ready, with a paper strip over the spine, I took careful measurements. That established the exact distance from the heights of the backed ridges on each side and the rounded spine. That data was translated into increments of one thousandths of an inch. For example, a book block with a bulk of 13/16 inch measured when rounded only .95 inches, after rounding and backing it showed 1.18.
That 1.18 equals roughly 1 3/16 inches for the width of the inlay. With this chart, it was possible to establish any cover dimension in a minute or two. Bear in mind, this was all done long before we had computers available. These days, once programmed, a cover size function is a matter of seconds. Best of all, if a Q.C. manager evaluates the finished bindings, some minor adjustments can always easily be made. (see chart below)
Now let us go back to our examples and calculate the requirement for a hardcover binding with a trim size of 6" x 9" and a bulk of 13/16 inch.
Cover dimensions 

Board size  57/8"  X  91/4" 
Joint area Inlay strip Joint area 
¼" plus 1 3/16" plus ¼" 

+ Board size  57/8"  
= Cover size  13 7/16"  x  91/4" 
+ Turnins (all four sides) 
5/8" plus 5/8" 
5/8" plus 5/8" 

Cover stock dimensions 
14 11/16" 
x 
< 10 ½" 
For heavy covering materials, allow a little more for the turnins.
The measurements used above are for Smythsewn book blocks. Adhesive bound books do not and should not be backed as much. Therefore deduct 1/16" of the width of the inlay, shorten the boards and increase the joints to 5/16". Again, all such data is most valuable to get a useful cover size program started. With minor adjustments made in time, it is perhaps one of a most useful tool for anyone who must produce quality hardcover bindings.
No matter what binding style you may produce, such a program is now even more important than ever. These days, most of the covering materials used are printed. The placements of the images are most often very critical. That is just one more reason why book covers must be calculated with an utmost precision, no matter if you are an edition, ondemand or photo book binding facility.
The following chart gives the width of inlay strip over a rounded and rounded and backed spine. The chart is derived from empirircal measurements
Book Bulk (inches) 
Rounded/backed (inches) 
Rounded only (inches) 
¼  0.43  0.28 
5/16  0.52  0.34 
3/8  0.59  0.41 
7/16  0.67  0.48 
½  0.75  0.56 
9/16  0.84  0.64 
5/8  0.92  0.72 
11/16  1.01  0.80 
3/4  1.09  0.87 
13/16  1.18  0.95 
7/8  1.27  1.03 
15/16  1.35  1.11 
1 inch  1.437  1.187 
1 1/16  1.52  1.27 
1 1/8  1.59  1.34 
1 3/16  1.67  1.42 
1 ¼  1.75  1.50 
1 5/16  1.88  1.58 
1 3/8  1.91  1.66 
1 7/16  1.98  1.72 
1 ½  2.06  1.81 
1 9/16  2.14  1.89 
1 5/8  2.22  1.97 
1 11/16  2.30  2.05 
1 3/4  2.37  2.12 
1 13/16  2.45  2.20 
1 7/8  2.53  2.28 
1 15/16  2.61  2.36 
2 inches  2.68  2.437 
2 1/8  2.84  2.58 
2 1/4/p>  2.98  2.72 
2 3/8  3.13  2.86 
2 ½  3.28  3.00 
2 5/8  3.43  3.14 
2 ¾  3.58  3.26 
2 7/8  3.78  3.42 
3 inches  3.87  3.56 