ISBN 10, ISBN 13, and Those Pesky X’s

(or…Get Your Info From Knowledgeable Sources)

A client wrote me sounding a teeny bit worried:

A friend of mine who used to be a bookstore manager mentioned the “X” that shows up after my ISBN number. She said it might be a problem when ordering books for the store because it indicated my book was Print on Demand. Is this a big concern or not?

I love the misinformation authors get from people who seem to know just enough about publishing to be dangerous. (This is what keeps agents in business.) I’m so glad my client asked me the question instead of needlessly worrying about it!

Here’s a bit of basic info about ISBNs:

The United States ISBN Agency is the only source authorized to assign ISBNs to publishers supplying the United States, U.S. Virgin Islands, Guam and Puerto Rico. There are over 160 other ISBN agencies throughout the world.

A new ISBN is required for each new or revised edition of a book. Once assigned, an ISBN can never be reused.

ISBNs used to be 10-digits. In 2007, they began the changeover to 13 digits. Publishers buy their ISBNs in huge blocks (they get a discount this way) and some books published today have ISBNs purchased before the 2007 changeover, so they have two ISBNs, a 10-digit and a 13-digit. You’ll notice the 13-digit version is simply the 10-digit one preceded by 978, and with a different final digit.

Sometimes an “X” appears—and what it actually means is “10.” Here’s why:

The ISBN has several parts which are all code for something. The final digit is known as the “check digit” and it verifies the ISBN. Check digits go from 0 to 10. In cases where the check digit would be 10, it appears as an X. The X only appears in 10-digit ISBNs.

The five parts of an ISBN are as follows (directly from the Bowker website,

1. The current ISBN-13 will be prefixed by 978.

2. Group or country identifier which identifies a national or geographic grouping of publishers.

3. Publisher identifier which identifies a particular publisher within a group.

4. Title identifier which identifies a particular title or edition of a title.

5. Check digit is the single digit at the end of the ISBN which validates the ISBN.

So there you have it. Learn something new everyday, I guess. Any more questions about boring topics like ISBNs?

Now, who can tell me what book I took the above ISBN image from?

© 2011 Rachelle Gardner, Literary Agent

Rachelle Gardner

Literary agent at Gardner Literary. Coffee & wine enthusiast (not at the same time) and dark chocolate connoisseur. I've worked in publishing since 1995 and I love talking about books!


  1. Mike DeBellis on January 27, 2014 at 12:59 PM

    Hi Rachelle:

    I just joined the Buffalo Writers Group network and need help in
    finding where to go to get ISBN numbers for my series of children’s books.

    I went on-line, but couldn’t tell who was legit…I only one that seemed real
    was Bowker.

    Do you know how I can get authentic & protected ISBN numbers

    My first book which is ready for distribution is called Charlie and the
    Cardboard Box.

    It’s about a little boy who needs to use a wheelchair and the target
    demographic is 3-9 year olds.

    I saw a void in the marketplace for books that kids with disabilities could
    relate to, so I wrote one.

    My oldest son is developmentally disabled and he was my inspiration for doing this.

    I hope you can help…


    Mike DeBellis

  2. Free Delay on August 26, 2011 at 9:29 AM

    Hi, I can’t understand how to add your site in my rss reader. Can you Help me, please.

  3. Jessica on February 23, 2011 at 10:13 PM

    >It's actually quite a fascinating algorithm to choose this "check sum/digit"!

    Simply take each number of the ISBN and multiply each interchangeably by 1 and 7, then add these products together. In this example (from the picture above) you would have:


    = 125

    Divide it by 10 and find the remainder–here, it would be 120 with a remainder of 5.

    5 is the check sum/digit. So you could see that if you ended up with a number/sum divisible by 10, it would instead be replaced by an X because if it were classified as a 0 in a database–such as in Excel–the database might be programmed to completely ignore it! (Like 14.0 is just seen as 14.) (: Too cool, huh?

  4. Sharon A. Lavy on February 22, 2011 at 7:43 AM

    >I did find that interesting. I may come back and look at this post again.

  5. Rachelle on February 15, 2011 at 3:45 PM

    >tom…ashville: If you're seeking publication from a publisher, then getting your own ISBN would be a collosal waste of time and money… because the publisher gets the ISBN, you don't. You can get ISBNs all day long for your unpublished works, but if you sell them to a publisher, the publisher can't use them, because the ISBN includes a code for the publisher..

    It would also cost you hundreds of dollars, whereas publishers can typically get them for as little as $1 because they buy ISBNs in bulk – thousands of them at a time.

    I can't help wondering why you would even consider this? Enlighten me. Seems like maybe it's just one more way to feel somehow either "official" or "protected" before publication. But an ISBN wouldn't offer either.

  6. Gwen Toliver on February 15, 2011 at 2:18 PM

    >Okay, obviously others figured the book title out first — which I'm glad for because it requires too much thinking right now. 🙂 Always appreciate helpful posts like this!!!

  7. Dustan on February 15, 2011 at 2:17 PM

    >Great information! Thanks a ton.

  8. Loree Huebner on February 15, 2011 at 12:59 PM

    >Thanks Rachelle. Your post cleared up a lot of questions I had on the subject.

  9. Katrina L. Lantz on February 15, 2011 at 12:48 PM

    >I didn't know any of that about ISBN's. Thanks for the info!

  10. Tamika: on February 15, 2011 at 12:48 PM

    >I'm with Catherine! I want to frame mine:) It will be a beautiful colleague of my dreams fulfilled!

  11. Timothy Fish on February 15, 2011 at 12:30 PM

    >I did a post on Do I Need an ISBN? a couple of months ago. Of course, the only reason an author needs to worry about that is if they are going to self-publish. Also, what an author thinks of as "a book" may have several ISBNs before the publisher is done with it.

  12. Cherie on February 15, 2011 at 12:27 PM

    >If you upload an ebook to Amazon or Barnes and Noble, you don't need an ISBN. It's always a good idea to get one, but you can publish and sell ebooks on both those sites without one.

  13. tom ... asheville, nc on February 15, 2011 at 12:09 PM

    >R …
    your daily posting are like taking Publishing 101 ! … thanks.
    question: is there any reason that i should or should not go ahead and get a number for completed work? (that has not yet been accepted by an agent or publisher.)
    thank TEH

  14. A.M. Kuska on February 15, 2011 at 11:51 AM

    >The most dangerous people in the world are the ones that have just a little bit of knowledge.

  15. redhead on February 15, 2011 at 10:46 AM

    >I remember doing a typo-laden post on ISBN's a while ago.

    It was mostly about finding specific editions via the isbn, and what to do if you are trying to Librarything your pre-1960s books that don't have isbns. . . .

  16. Fiction Chick on February 15, 2011 at 10:44 AM

    >What great info, Rachelle. So does getting assigned an ISBN mean the book is "published" for legal purposes?

  17. lynnrush on February 15, 2011 at 10:43 AM

    >Wow. Very interesting stuff here. Had no idea about the ISBN things. Great stuff here.

  18. Casey on February 15, 2011 at 10:37 AM

    >I don't know if this counts or not…but I looked up it up in the Goodreads search engine. 🙂 Snow Day by Billy Coffey.

    Very interesting on ISBN's I had never thought about those things before, but had wondered on occasion. 🙂

  19. Nic on February 15, 2011 at 10:18 AM

    >i sort of knew a bit about this already through computing.

    In any digital signal you have a check bit or a parity bit or in case of larger blocks of data a byte. These are generally used to check whether there has been an error in transmission & decoding. In case of ISBN's i assume its to make sure the ISBN has been read correctly. Its usually calculated using the other numbers in the sequence.

  20. Bonita on February 15, 2011 at 9:44 AM

    >The book: Snow Day by Billy Coffey

    Am I right?

  21. Timothy Fish on February 15, 2011 at 8:38 AM


    Even though we've officially moved to 13 digits, the old 10 digit ISBNs haven't been completely used up. To transition from 10 to 13, numbers were added to the 10 numbers to convert them to 13 digits. Any 13 digit ISBN that has these numbers added on can be converted back to the 10 digit equivalent. Once the ISBN registrars begin giving out the new numbers, this conversion will not be possible.

  22. Rachelle on February 15, 2011 at 8:37 AM

    >Katy: That's right, only books intended for retail sale (including e-books) need ISBNs. If you are only selling through a personal, private distribution system (ie your own website) or giving the book away, you don't need an ISBN. But if you're going to sell through Amazon or any other distributor or retail outlet, ISBNs are required.

    Weirdmage: If Amazon or anyone else lists a 10-digit ISBN for a book (along with the 13-digit), that means those books do indeed have a 10-digit ISBN. A retailer can't just "make up" an ISBN. But since all books must have 13-digit ISBNs now, you won't see any listings for new books with ONLY a 10-digit. If they were originally issued a 10-digit, they will ALSO have a 13-digit. Nobody's converting or making up ISBN numbers.

  23. Weirdmage on February 15, 2011 at 8:17 AM

    >What I've never understood is why Amazon, Goodreads etc convert 13 digit ISBN numbers to 10 digit numbers and post them too.
    Can someone explain why, and how this works, since these books don't actually have a 10 digit ISBN number?

  24. Heather Webb on February 15, 2011 at 7:53 AM

    >So the "Chris" comment was actually me. My husband never logged out. Grrrrr.

  25. chris on February 15, 2011 at 7:50 AM

    >It's frustrating having so many people with misinformation. It makes learning the business a daunting task at times. I appreciate that you clear up so many of the myths on your blog.

  26. Timothy Fish on February 15, 2011 at 7:47 AM

    >Actually, check digits go from 0 to 10, rather than 1 to 10, which is why the X is necessary. Also, the X does not exist for ISBN-13 because the check digit is calculated differently.

    As others have mentioned, there’s something special about having that number to identify a book. It’s at that point that the book goes from being just something sitting on our computer to being something that the rest of the world knows about. My favorite at the moment is 978-1-61295-000-6.

  27. Anna Zagar on February 15, 2011 at 7:29 AM

    >Thanks Rachelle! I'm trying to soak up as much as possible about the whole process and ISBN's intimidated me. Thanks for breaking it down. How exciting to have your own ISBN! Would it be nerdy to memorize it?

  28. Catherine West on February 15, 2011 at 7:28 AM

    >Ha. I didn't actually care what all the numbers meant – to me, they only say one thing.
    I'm framing mine.

  29. Sue Harrison on February 15, 2011 at 7:17 AM

    >Thank you! I've wondered about ISBNs. And thank you to Katie, because I had no idea what the initials stood for!

  30. Katie Ganshert on February 15, 2011 at 6:11 AM

    >International Standard Book Number – in case somebody else didn't know. 🙂

  31. Katie Ganshert on February 15, 2011 at 6:09 AM

    >It just hit me that I'm going to have my own ISBN number!

    What does ISBN stand for anyway? Or is that something most writerly folk know? I'm going to go Google it.

  32. Katy McKenna on February 15, 2011 at 6:01 AM

    >One addition, and I'm sure this is obvious: If you happen to be self-publishing a book which will never be offered for sale, you do not have to purchase an ISBN number for that book. We gave my mother-in-law her favorite gift ever for her 82nd birthday–100 volumes of a book of her own poetry (print-on-demand) for her to give away to family, friends, and acquaintances at the nursing home. We knew this book would never be sold, only given away, so we did not add the considerable expense of the ISBN. She was never so excited as when we went into a second printing of another 100 books!!! Happiest Lady Who Never Had An ISBN Number!

  33. Pranavam Ravikumar a.k.a. Kochuravi on February 15, 2011 at 5:50 AM

    >Great Info!

  34. Rosemary Gemmell on February 15, 2011 at 4:23 AM

    >I'm not a numbers person either – but it makes a difference when it's the numbers on the back of a published book! Thanks for making us the most informed blog readers in any country, Rachelle.

  35. Aimee L Salter on February 15, 2011 at 2:14 AM

    >I'm with Tana.


  36. Tana Adams on February 15, 2011 at 1:08 AM

    >Rarely do number have the power to excite me. (Sometimes on a clearance rack, but that’s besides the point.) ISBN numbers however thrill me. The fact that one day my novel will have its very own bar code in this world warms my heart.

  37. Vicki on February 15, 2011 at 12:31 AM

    >Wow, that's pretty spiffy. Thanks for the cool info!

  38. Liralen on February 15, 2011 at 12:28 AM

    >"Snow Day: A Novel" – Billy Coffey.

  39. Roxane B. Salonen on February 15, 2011 at 12:25 AM

    >Rachelle, is that a trick question? 🙂

  40. Josin L. McQuein on February 15, 2011 at 12:03 AM

    >Ugh. It sounds like Social Security Number coding.

    And according to Google, the book is Snow Day.