ISBN-10 is a 10-digit book identifier used before 2007; ISBN-13 is the current 13-digit standard that replaced it. The two formats differ in length, structure, and how they fit into the retail supply chain, but every ISBN-10 can be converted to an ISBN-13. Self-published authors only need ISBN-13s for new books; ISBN-10 is no longer assigned and functions today as a legacy lookup number.
- What Changed in 2007 and Why Did the ISBN Get Longer?
- How Do ISBN-10 and ISBN-13 Differ in Structure?
- Can You Convert an ISBN-10 to an ISBN-13?
- What Is the 979 ISBN Prefix and Why Does It Matter?
- What Is the Difference Between an ISBN and an ASIN?
- Do You Still Need Both ISBN-10 and ISBN-13?
- Frequently Asked Questions
What Changed in 2007 and Why Did the ISBN Get Longer?
On 1 January 2007, the publishing industry switched from 10-digit ISBNs to 13-digit ISBNs. The International ISBN Agency coordinated this transition by updating the ISO 2108 standard.
Two problems forced the change. First, the 10-digit numbering space was running out of available combinations in several registration groups, particularly in English-language markets where publishing volume had grown rapidly through the 1990s and 2000s. Second, ISBN-10 was incompatible with the 13-digit European Article Number (EAN) barcode system used for every other retail product in the world. Books existed in a parallel numbering universe that retailers, distributors, and library systems had to handle separately.
The solution was to bring books into the global EAN system by adding a three-digit prefix (978, known as “Bookland”) to every existing ISBN-10 and recalculating the final digit (called the check digit, explained below). This made every book’s identifier scannable by the same barcode infrastructure that handles groceries, electronics, and clothing. After 1 January 2007, no new ISBN-10 numbers were assigned; all new ISBNs are 13 digits long.
How Do ISBN-10 and ISBN-13 Differ in Structure?
Both ISBN formats are built from the same core pieces of information, arranged in a specific order. Before looking at the differences, here is what each piece means:
- Registration group: identifies the language or country. For example, “0” and “1” are assigned to English-language publishers.
- Registrant: identifies the publisher. Larger publishers get shorter registrant numbers, which leaves more digits for their individual titles.
- Publication: identifies the specific title and edition. Each format of a book (paperback, hardcover, ebook) gets its own publication number.
- Check digit: a single digit at the end, calculated from all the other digits using a set formula. Its only job is to catch typos; if someone mistypes a digit, the check digit will not match and the error is flagged.
The difference between the two formats is that ISBN-13 adds a prefix (978) at the beginning and uses a different formula to calculate the check digit. ISBN-10 has no prefix; ISBN-13 always starts with one. The table below summarises the key differences.
| Feature | ISBN-10 | ISBN-13 |
|---|---|---|
| Length | 10 digits | 13 digits |
| Prefix | None | 978 (a second prefix, 979, is covered below) |
| Check digit algorithm | Modulus-11 (can produce “X”) | Modulus-10 (always 0-9) |
| Barcode compatibility | Required conversion for EAN | Native EAN-13 |
| Still assigned to new books? | No (stopped 1 Jan 2007) | Yes |
The next two sections walk through the arithmetic behind each check digit formula. As an independent author, you do not need to know or do any of this; just make sure you copy and paste your assigned ISBN correctly and the check digit takes care of itself. That said, when I started working in publishing in 1986, we used to verify check digits with a pen and paper, and the maths still fascinates me. So geek out with me below, or skip ahead to the conversion section.
How the ISBN-10 check digit works (modulus-11)
Each of the first nine digits is multiplied by a descending weight from 10 down to 2. The products are added together, and the check digit is whatever value makes the total evenly divisible by 11. Because the result can sometimes be 10, the letter “X” is used to represent it (since a single digit cannot be 10).
Here is a worked example using the ISBN-10 0-306-40615-2:
| Position | Digit | Weight | Product |
|---|---|---|---|
| 1 | 0 | × 10 | 0 |
| 2 | 3 | × 9 | 27 |
| 3 | 0 | × 8 | 0 |
| 4 | 6 | × 7 | 42 |
| 5 | 4 | × 6 | 24 |
| 6 | 0 | × 5 | 0 |
| 7 | 6 | × 4 | 24 |
| 8 | 1 | × 3 | 3 |
| 9 | 5 | × 2 | 10 |
Sum of products: 0 + 27 + 0 + 42 + 24 + 0 + 24 + 3 + 10 = 130. Divide 130 by 11: that gives 11 remainder 9. The check digit is 11 − 9 = 2. So the full ISBN-10 is 0-306-40615-2. If someone accidentally typed a wrong digit anywhere, the check would fail, flagging the error.
How the ISBN-13 check digit works (modulus-10)
The first 12 digits are multiplied by alternating weights of 1 and 3 (first digit × 1, second × 3, third × 1, and so on). The products are summed, and the check digit is whatever makes the total divisible by 10. This is the same algorithm used for all EAN-13 retail barcodes, which is the whole reason the ISBN was extended to 13 digits.
Here is a worked example using the ISBN-13 978-0-306-40615-7 (the 13-digit equivalent of the ISBN-10 above):
| Position | Digit | Weight | Product |
|---|---|---|---|
| 1 | 9 | × 1 | 9 |
| 2 | 7 | × 3 | 21 |
| 3 | 8 | × 1 | 8 |
| 4 | 0 | × 3 | 0 |
| 5 | 3 | × 1 | 3 |
| 6 | 0 | × 3 | 0 |
| 7 | 6 | × 1 | 6 |
| 8 | 4 | × 3 | 12 |
| 9 | 0 | × 1 | 0 |
| 10 | 6 | × 3 | 18 |
| 11 | 1 | × 1 | 1 |
| 12 | 5 | × 3 | 15 |
Sum of products: 9 + 21 + 8 + 0 + 3 + 0 + 6 + 12 + 0 + 18 + 1 + 15 = 93. Divide 93 by 10: that gives 9 remainder 3. The check digit is 10 − 3 = 7. So the full ISBN-13 is 978-0-306-40615-7.
Can You Convert an ISBN-10 to an ISBN-13?
Yes, but only in one direction with certainty. Every ISBN-10 can be converted to an ISBN-13 by dropping the old check digit, prepending “978,” and recalculating the check digit using the modulus-10 algorithm. The reverse (ISBN-13 to ISBN-10) works only for ISBNs that begin with the 978 prefix; you strip the prefix, drop the ISBN-13 check digit, and recalculate using modulus-11.
ISBNs beginning with the 979 prefix cannot be converted back to ISBN-10 at all. The 979 prefix has no 10-digit equivalent because it was created after the transition; the entire 979 numbering space exists only in 13-digit form. This distinction matters because Bowker (the US ISBN agency) has been issuing 979-prefixed ISBNs since 2020, and an increasing share of newly purchased ISBNs start with 979.
For practical purposes, self-published authors rarely need to convert manually. Retailers, distributors, and library catalogue systems handle the conversion automatically. If you have an older book with only an ISBN-10 printed on the copyright page, the corresponding ISBN-13 is already in every database that matters.
What Is the 979 ISBN Prefix and Why Does It Matter?
The 979 prefix is the second “Bookland” prefix, activated because the 978 numbering space is being depleted. Bowker began issuing 979-prefixed ISBNs to US publishers in early 2020. The key difference for authors: a 979-prefix ISBN has no ISBN-10 equivalent and cannot be converted to one.
This created some early compatibility concerns. Older inventory systems that stored only 10-digit ISBNs could not process 979-prefix books at all. As of 2025, the major platforms have resolved these issues. Amazon KDP supports 979-prefix ISBNs (KDP’s own free ISBNs start with 979-8). IngramSpark fully supports 979-prefix ISBNs for distribution. Library systems including OCLC and WorldCat catalogue 979-prefix titles without issue.
If you buy a block of ISBNs from Bowker today, some or all of them will likely start with 979. This is normal and does not limit your distribution options. The only practical implication is that these ISBNs will never have a 10-digit shorthand, which is increasingly irrelevant since no major system requires ISBN-10 for new titles.
What Is the Difference Between an ISBN and an ASIN?
An ISBN is a global book identifier managed by the International ISBN Agency and recognised by every bookstore, library, and distributor worldwide. An ASIN (Amazon Standard Identification Number) is Amazon’s proprietary 10-character alphanumeric code assigned to every product on their marketplace, not just books.
Every book listed on Amazon gets an ASIN regardless of whether it has an ISBN. For Kindle ebooks published through KDP, the ASIN is the primary identifier; an ISBN is optional and has no effect on Amazon discoverability. For print books (paperback and hardcover), an ISBN is required. If you do not provide your own, KDP assigns a free one with the 979-8 prefix, but “Independently published” appears as the publisher of record and the ISBN cannot be used outside Amazon.
A common point of confusion: authors who purchase their own ISBN and enter it during KDP setup sometimes wonder why their book also has an ASIN. Both identifiers coexist. The ISBN is for the global supply chain; the ASIN is for Amazon’s internal catalogue. They serve different purposes and neither replaces the other.
| Feature | ISBN | ASIN |
|---|---|---|
| Scope | Global (all retailers, libraries, distributors) | Amazon only |
| Format | 13 digits (numeric only) | 10 characters (alphanumeric) |
| Required for KDP ebooks? | No | Yes (auto-assigned) |
| Required for KDP print? | Yes (free from KDP or purchased: in the US, $125 single / $295 for 10 from Bowker) | Yes (auto-assigned) |
| Portable across platforms? | Yes (if you own it) | No |
Do You Still Need Both ISBN-10 and ISBN-13?
No. Self-published authors publishing new books need only ISBN-13. ISBN-10 is not assigned, not required by any platform, and not needed for any distribution channel. The question “do I need both?” comes up because older books sometimes display both numbers on the copyright page, and some online retailers still show both in their catalogue listings for pre-2007 titles.
Here are the scenarios self-published authors encounter most often:
Publishing a new book on KDP only
You do not need to purchase an ISBN at all for a Kindle ebook; Amazon assigns an ASIN. For a KDP paperback or hardcover, you can accept KDP’s free ISBN, but this locks the book to Amazon and lists “Independently published” as the publisher. If you want control over your imprint name or plan to distribute elsewhere later, purchase your own ISBN-13 from Bowker ($125 for a single ISBN, $295 for a 10-pack).
Distributing wide (IngramSpark, Draft2Digital, bookstores, libraries)
You need your own ISBN-13. Free ISBNs from KDP or IngramSpark are tied to those platforms and cannot be used elsewhere. A purchased ISBN-13 is portable across every distribution channel and lists your chosen imprint as the publisher of record.
Reprinting an older book that only has an ISBN-10
If the content is unchanged, you do not need a new ISBN. The ISBN-10 to ISBN-13 conversion is handled automatically by every major retailer and distributor. The 978-prefixed ISBN-13 equivalent already exists in their systems. You can print both numbers on the copyright page for clarity, but only the ISBN-13 goes on the barcode.
Publishing a new edition of an existing book
A new edition with substantial changes (revised text, added chapters, new cover design) requires a new ISBN-13. Minor corrections (fixing typos, adjusting spacing) do not require a new ISBN. The distinction matters because retailers use ISBNs to differentiate editions; if you reuse an old ISBN for a substantially revised book, the original and revised versions become indistinguishable in the supply chain.
Publishing in multiple formats
Each format needs its own ISBN-13: one for the ebook, one for the paperback, one for the hardcover, and one for the audiobook. This is an International ISBN Agency requirement, not a platform-specific rule. The rationale is that each format is a distinct product with its own pricing, distribution, and metadata.
Frequently Asked Questions
Does the ISBN-13 replace the ISBN-10 on my book’s barcode?
Yes. All book barcodes use the ISBN-13 encoded as an EAN-13 barcode (commonly called a Bookland EAN). ISBN-10 has not been used for barcode generation since the 2007 transition. If your book was published before 2007 and you are reprinting it, update the barcode to show the ISBN-13 equivalent. The ISBN-10 can still appear on the copyright page as a secondary reference, but the barcode must be ISBN-13.
Do ebooks need an ISBN-13?
It depends on where you distribute. Amazon KDP does not require an ISBN for Kindle ebooks; the ASIN serves as the identifier. However, Apple Books, Kobo, Barnes & Noble Press, and Google Play Books either require or strongly recommend an ISBN-13. If you plan to distribute your ebook beyond Amazon, you need one.
Where do I find my book’s ISBN-10 or ISBN-13?
Check the copyright page (usually the verso of the title page), the back cover near the barcode, or your publishing dashboard (KDP Bookshelf, IngramSpark title management, or your Bowker myidentifiers.com account). Amazon product pages for older titles may display both the ISBN-10 and ISBN-13 in the “Product Details” section.
How is the ISBN-13 check digit calculated?
Take the first 12 digits of the ISBN-13 and apply alternating weights of 1 and 3 (first digit multiplied by 1, second by 3, third by 1, and so on). Sum the 12 products. The check digit is whatever number, when added to that sum, makes the total divisible by 10. For example, if the sum of the weighted digits is 93, the check digit is 7 (because 93 + 7 = 100). This modulus-10 algorithm is the same one used for all EAN-13 barcodes.
Is ISBN-10 still accepted anywhere for new books?
No. No ISBN agency assigns ISBN-10 numbers, and no major retailer, distributor, or library system requires or accepts an ISBN-10 as the primary identifier for a new title. ISBN-10 persists only as a legacy reference for books published before 2007. Some databases and retailer catalogue pages still display ISBN-10 alongside ISBN-13 for older titles, but this is a display convenience, not a requirement.
