What in the World is an ISBN, Anyway?

For any author, making sure people can find your book is one of the essential elements of success (maybe second only to actually writing a book). It sounds much simpler than it is, of course; the main challenge of self-publishing is the self-promotion and marketing.

With all of the work involved in self-publishing a book, it could be tempting to trim down the process. While we’re all for making life easy there’s one element no author should skip: the ISBN.

An ISBN (short for “International Standard Book Number”) is a unique, 13-digit code on all published books. As their name implies, ISBNs are used worldwide to identify titles, editions, reprints, etc. We see them on books every single day without paying them much attention, but these numbers are very deliberate and extremely important to authors all over the world.

How Does an ISBN Work?

The 13 digits of each ISBN aren’t just a random collection of numbers, but specific values based on where you are, who publishes your book, their output and even some complicated math.

Five elements make up the 13 digits of each ISBN:

  • Prefix Element
  • Registration Group Element
  • Registrant Element
  • Publication Element
  • Check Digit

Prefix Element - 3 digits

The prefix element is fixed in length, always representing the first three digits. Currently there are only two possible prefixes: 978 and 979. These numbers are “released” by EAN International and as the need for more ISBNs arises, more will be made available to increase the capacity of the system.

Registration Group Element - 1 to 5 digits

This second element is a national, geographic or language identifier. Here in the United States, we fall into a ‘language group’ with other English speaking countries (using the identifiers 0 and 1), while a book published in Turkey would carry the national identifier 605.

Registrant Element - up to 7 digits, and Publication Element - up to 6 digits

The registrant element identifies the publisher or imprint of the title, while the Publication element identifies the edition by the publisher. Because every ISBN is limited to 13 digits, the lengths of these two elements are very closely tied.

Publishers or imprints with high anticipated outputs (read: lots and lots of titles) will have shorter Registrant Elements in order to allow for more digits in the Publication Element. Smaller publishers will have longer Registrant Elements because they will not have as many titles and thus, not require as many digits in the Publication elements.

In cases where a combination of the five elements would have fewer than 13 digits, leading zeros are added to the Publication element to bring the ISBN to the correct length.

Check Digit - 1 digit

The fifth and final element of ISBNs is the Check Digit, which is a single number calculated from the other digits before it.

Starting from the beginning, each of the first 12 digits is alternately multiplied by 1 or 3. These numbers are added together and divided by 10. The remainder is subtracted from 10, and that result is the check digit. (If the final result is ’10’, the Check Digit is a 0.)

If this explanation of the check digit wasn’t confusing enough, Wolfram MathWorld has a terrifyingly technical explanation.

The final product is a unique, 13-digit code for your book, with each element separated from the next using hyphens.

How Do You Get an ISBN?

In the United States, Bowker operates isbn.org which makes it easy for authors to purchase any number of ISBNs (starting at $125 for one), and even has special packages incorporating some additional services, all designed with the self-publisher in mind.

For international authors, you can find your ISBN agency here. 

Why Do You Need an ISBN?

Many retailers actually use a book’s ISBN to help track inventory, making it crucial for a title that will (or hopefully will) be commercially sold. Even the simple act of buying an ISBN is a valuable step towards distribution.

RR Bowker, the company in charge of issuing ISBNs in the United States, keeps a database, updated daily, with every book that is currently print, and even those that are set to publish up to six month in advance.

In a database of 3.4 million books one title can seem like a mere drop in the bucket, but when users and companies can search the bucket for individual drops, it’s worth it. Bowker’s Books in Print database is accessed by libraries, retailers, Google Books, Apple iBooks, and other major book-buying avenues. If you’re planning to sell your book commercially, you will want and NEED to have an ISBN assigned to your title.

If you have a question about ISBNs, please leave it in the comments below and a member of Team Steuben will get back with you - we love sharing our knowledge with self-publishers!

Adam user

President & CEO,
Steuben Press

Adam Ellis has worked in the book industry since 2002, when he was first exposed to the wonderful world of Self Publishing. Over the years he has worked with thousands of authors and helped to produce, print and publish countless books.

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