At first glance, International Standard Book Numbers (ISBNs) appear to be nothing more than a random string of numbers, serving little or no purpose. But, believe it or not, these codes express important details about a book, like its publisher, region, and edition, all within just 13 digits.
Let's discuss the language of ISBN numbers and what five key elements they communicate.
Brief Overview
International Standard Book Numbers (ISBNs) are 10- to 13-digit codes that identify a particular book, or version of a book, when dealers, libraries, or just about anyone searches its designated ISBN number. Every nonserial, traditional book requires an ISBN, including books that are part of a nonserial series. What makes a release nonserial is the lack of a preset installment schedule—monthly, weekly, or otherwise—as well as an understanding that these series are bound to end at some point.
The 13-Digit Code
ISBNs are represented by a 13-digit code which allows publishers, retailers, and other suppliers to directly identify an individual product. Identifiers become particularly useful when maintaining stock, listing new releases, placing an order, or tracking sales figures.
Behold, here is an example ISBN:
978-92-95055-02-5
Within these 13 digits, there exists five segments—which we’ve broken down below—that communicate five separate, important elements about the nonserial book it represents.
Prefix (Example Above: 978)
This three-digit element makes an ISBN number compatible with the European Article Number (EAN) system.
Effective Jan. 1, 2007, ISBNs were upgraded from 10 digits to 13 digits, specifically to include this introductory, three-digit code. By doing so, books have become an official EAN product, effectively integrating ISBNs into the EAN system. EAN codes are very similar to Universal Product Codes (UPCs)—the U.S. equivalent—except EANs remain common for identifying products retailed internationally that aren’t produced within the United States.
Prefix elements remain limited to two possible choices—978 or 979. For typical products, these prefixes represent the country of origin. All books, however, fall under the same, fictitious classification—Bookland. This was essentially seen as a quick, easy workaround to convert ISBNs into EANs without confusing the overarching system.
Registration group (Ex. 92)
This element identifies the book’s country of origin. Sometimes that term— ‘country of origin’—isn’t inclusive enough, so this element can also identify the geographic region. In short, these one to five digits answer a very simple question—where on the map was this book initially registered by the publisher, or registrant?
Registrant (Ex. 95055)
This element identifies the publisher listed as the book’s registrant. Just to clarify, we’re essentially making our way down a checklist—‘registration group’ accounts for where, ‘registrant’ accounts for who.
When registering an ISBN, publishers must also go down a checklist, supplying all pertinent information about their identity, location, etc. Such details end up here, hidden within an ISBN code, as a five-digit sequence that computers can then decipher and employ accordingly.
Publication (Ex. 02)
No, this element doesn’t address the actual publisher and/or publication under which a book is released, but, rather, the edition and format of this ISBN’s specific book.
So, we’ve now covered all the bases–who, where, and what–with ‘publication’ accounting for what version of this book our ISBN represents. Each edition, version, or format of a book receives its own ISBN number, letting the computer know what specific, let’s say, Harry Potter and the Chamber of Secrets product is being processed.
Is this book hard or soft cover? Is this book a first or third edition? Is this book, perhaps, an eBook or audiobook? Computers need answers to these questions, and, thankfully, ISBNs provide them through this ‘publication’ element.
Check digit (Ex. 5)
This element validates all prior elements, ensuring that the ISBN number in question is, indeed, legitimate. How? Well, whenever an ISBN is suspect, there’s an equation that’s used to check the previous four elements. This ‘check digit’ can then assess if the code is correct.
Below is an example ‘check digit’ equation, using the ISBN number from earlier: 978-92-95055-02-5.
9 (1) + 7 (3) + 8 (1) + 9 (3) + 2 (1) + 9 (3) + 5 (1) + 0 (3) + 5 (1) + 5 (3) + 0 (1) + 2 (3)
The sequence’s last digit, or ‘check digit’, is put aside – in this case 5 – leaving behind 12 of those initial 13 digits. All 12 digits are then added together, but only after being properly weighted. ISBN Information states that a “13-digit ISBN uses weights of 1 and 3 alternately, six times over, for the 12-digits prior to the check digit.”
9 (1) + 7 (3) + 8 (1) + 9 (3) + 2 (1) + 9 (3) + 5 (1) + 0 (3) + 5 (1) + 5 (3) + 0 (1) + 2 (3)
9 + 21 + 8 + 27 + 2 + 27 + 5 + 0 + 5 + 15 + 0 + 6 = 125
From there, divide the total by 10 as many times as possible, until left with a remainder between 0 and 9. If the remainder is 0, then the ‘check digit’ should, likewise, be 0. If not, take the number 10 and subtract your remainder from it. That total should match the ‘check digit’ we put aside earlier.
125 / 10 = 12 remainder 5
10 – 5 = 5
So, yes, we’ve just proven that our ISBN number is, indeed, legitimate.
To learn more information about ISBNs, check out CIP, ISSN, ISBN—What’s the Difference?