Publishers often need the physical dimensions of a book before it is actually printed: in particular, the spine width for laying out the cover and the weight of the finished book for estimating shipping costs. This post demonstrates the relatively simple math involved in making these calculations. If you want to skip the math lesson, you can use our online calculators.
- Calculating spine width
(Online spine width calculator is here.)
- Calculating the weight of a book
(Online book weight calculator is here.)
The spine width of your book is important to know because it allows you to accurately lay out the cover file for printing. The spine width of a paperback book is dependent on three things:
- The number of pages, including roman-numeraled frontmatter pages and blank pages.
- The thickness of the paper, expressed in pages per inch (PPI).
Your printer should provide the PPI for any paper they quote printing on.
- An allowance for the thickness of the cover.
This allowance should also be provided by your printer. We use .0156″, which assumes the cover is printed on 10-point coated-one-side stock, the standard, and is laminated.
The formula for calculating spine width is:
Spine width = (Pagecount / PPI) + Cover thickness allowance
Here’s an example:
A book has 316 pages, is to be printed on a 400-ppi paper stock, and the printer has given you an allowance of .0156 inches for the thickness of the cover. Let’s calculate that step by step:
Spine width = (Pagecount / PPI) + Cover thickness
Spine width = (316 pages / 400 ppi) + .0156
Spine width = .79 + .0156
Spine width = .8056″
A decimal value for inches isn’t very useful, but it is easy to convert to fractional inches by multiplying the decimal fraction by 32 to get the spine width in thirty-seconds of an inch:
.8056 x 32 = 25.779 sixteenths
Round 25.779 to 26 and you get 26/32-inch, which simplified is 13/16, so
Spine width = 13/16″
Because binder tolerance is around 1/32″ and actual paper thickness varies with humidity and temperature, rounding to the nearest 32nd of an inch is fine. Your printer should fine tune the spine width if it is necessary, without you even asking: you can check the result on the cover proof they provide.
The same formula works for high page count books as well. Here’s an example:
A book has 840 pages, is to be printed on a 400-ppi paper stock, and the printer has given you an allowance of .0156 inches for the thickness of the cover. Here are the calculations:
Spine width = (Pagecount / PPI) + Cover thickness
Spine width = (840 pages / 400 ppi ) + .0156 cover thickness
Spine width = 2.1 + .0156
Spine width = 2.1156″
Multiply just the part to the right of the decimal point by 32 to get fractional inches:
.1156 x 32 = 3.6992 sixteenths
Round the thirty-seconds:
3.6992 thirty-seconds rounded is 4/32 inch, which simplified is 1/4
Add in the whole number to the left of the decimal point (the 2 in 2.1156):
2 + 1/4 = 2-1/4″ spine width
In the U.S., hard cover boards usually add about 1/4″ to the width of a spine, so this same 840-page book would have a spine width of 2-1/2″ as a hardcover:
2 + 1/4 + 1/4 = 2-1/2
This is useful for sizing foil stamp art for the spine, but dust jackets are notoriously tricky to size because of the joints at the spine and the way that jackets wrap around the boards. We highly recommend getting dust jacket measurements from your printer. You can also do this for your paperback covers.
Calculating the weight of a book is a little more involved than calculating the spine width. Weight so calculated is rarely spot-on, but it can be useful estimating shipping costs when you are budgeting a book project, especially if you are sending out single copies.
The weight of a book depends on these factors:
- Number of pages, including roman-numeraled frontmatter and any blanks.
- Page size.
- Paper density, as measured in basis weight (U.S.) or grammage (metric).
- An allowance for the cover weight.
Here’s a simplified formula for calculating the weight of a paperback using basis weights.
Book weight = ((Basis weight ÷ 950,000) × Page width × Page height × Page count) + .06
- Basis weight is the standard measurement of the paper’s density. The “basis weight” of a 60-lb. stock is 60-lb.
- 950,000 is the number of surface square inches in a ream of text stock at the basis weight sheet size (25 x 38).
- .06 is an allowance for the weight of the cover, glue and lamination. This is based on a 6″ x 9″ book with a 1″ spine: you can nudge this value up or down for larger or smaller page sizes.
Here’s an example
A book has 316 pages, and is to be printed on a 60-lb. paper stock, with a paperback cover printed on 10-point coated one side stock and laminated. The book’s page size is 6″ wide by 9″ high. Let’s calculate the weight step by step:
Weight = ((60 ÷ 950,000) × 6 × 9 × 316) + .06
Weight = 1.0778 + .06
Weight = 1.1378 lbs.
As with inches, a decimal value for pounds isn’t very useful, but it is easy to convert to ounces by multiplying the decimal fraction by 16:
.1378 x 16 = 2.2048 oz.
Rounded: 3 oz. (Always round up: that’s what UPS and the USPS will do!)
Add back in the whole number from the decimal weight calculated above and you get:
book weight = 1 lb. 3 oz.
Need a printing quote or more information?
I’d be happy to answer questions—you can contact me via email.
Don Leeper is founder and CEO of Bookmobile, which has provided design, printing, eBook and distribution services for book publishers since 1982.