Every book published since 2007 needs an ISBN-13. Here's what that means for an older ISBN-10, how to convert it, and why 979 numbers can't go back.
If you have a 10-digit ISBN from an older book, or a form in front of you asking for one, here is the short answer. Every ISBN issued since 1 January 2007 has 13 digits. A 10-digit number from before then is still valid, but it should be recorded and quoted in its 13-digit form, which you get by putting 978 in front and recalculating the last digit. If your ISBN starts with 979, it has never had a 10-digit form and never will.
Getting this wrong has real costs. Type an ISBN-10 into a system that expects 13 digits and the lookup fails. Convert a 979 number by hand and you produce a number that belongs to a different book, or to nobody, which is how duplicate listings and misdirected orders start.
The ISBN became an ISO standard in 1970 with 10 digits, and for over 30 years that was enough. Two pressures changed it. The first was capacity. The second was barcodes. Retail scanners read 13-digit EAN codes, and under an agreement with EAN International the book trade was already printing the ISBN as an EAN-13 barcode by putting 978 in front of it. The 2005 revision of the standard made the 13-digit number the ISBN itself. From 1 January 2007, national agencies only issue 13-digit numbers. The International ISBN Agency's manual says the change increased the system's capacity and made the ISBN "completely compatible with the GS1 GTIN-13", the standard retail product code.
The extra room comes from a second prefix, 979. Every 13-digit ISBN starts with one of the two. The 978 space is the old 10-digit space with a prefix on the front. The 979 space is new.
An ISBN-10 has four parts: a registration group that identifies a country or language area, a registrant element that identifies the publisher, a publication element for the specific edition and format, and a check digit. An ISBN-13 has the same four parts plus a three-digit prefix at the front, 978 or 979.
| ISBN-10 | ISBN-13 | |
|---|---|---|
| Length | 10 digits | 13 digits |
| Parts | Group, registrant, publication, check digit | Prefix (978 or 979) plus the same four |
| Check digit | Modulus 11, weights 10 down to 2, X stands for 10 | Modulus 10, weights alternate 1 and 3 |
| Issued | Until 31 December 2006 | Since 1 January 2007 |
| Converts to the other | Always, by adding 978 and recomputing the check digit | Only when it starts with 978 |
| Where you still see it | Older books, Amazon pages for 978 titles, legacy forms | Barcodes, catalogues, every retailer system |
The last digit of an ISBN is not part of the book's identity. It is a checksum that lets a scanner or a form catch a typo. The two formats calculate it differently.
Take the 1981 Springer hardcover Error-Correction Coding for Digital Communications, ISBN-10 0-306-40615-2. For an ISBN-10, multiply the first nine digits by 10, 9, 8 and so on down to 2, then add the products. The check digit is whatever brings the total to a multiple of 11. Here the weighted sum of the first nine digits is 130. The next multiple of 11 is 132, so the check digit is 2. When the missing amount is 10, the check digit is written as X, which is why some older ISBNs end in a letter.
For an ISBN-13 the rule comes from the current ISBN Users' Manual: multiply the first 12 digits alternately by 1 and 3, add the products, divide by 10, and subtract the remainder from 10. A result of 10 counts as 0. For 978-0-306-40615 the weighted sum is 93, the remainder is 3, and the check digit is 7. The same book is therefore 978-0-306-40615-7 as an ISBN-13. Same identifier, different last digit.
Drop the old check digit, put 978 in front of the remaining nine digits, and calculate a new check digit with the modulus 10 rule above. That is the whole conversion, and it is what our ISBN converter does in either direction for 978 numbers. If you want to confirm a number is intact before you put it on a form, the ISBN validator checks the check digit at both lengths.
An old book does not need a new ISBN. The 13-digit form is the same identifier with a prefix, so the title, edition and publisher behind it are unchanged. A new edition or format is different and needs its own ISBN.
Numbers starting with 979 were opened up after the switch, so they have only ever existed at 13 digits. Strip the prefix from a 979 number and compute a modulus 11 check digit and you get a 10-digit string that either belongs to a different 978 book or to nobody. The International ISBN Agency's notice on US prefixes puts it plainly: a 979 ISBN "is not backwards compatible and does not have an equivalent 10-digit ISBN", and trying to convert one "will bring serious errors including duplicated ISBNs and incorrect supply of orders".
For US authors this is now routine. Bowker, the US ISBN agency, began issuing 979-8 numbers in early 2020 as its 978 stock ran low, and every ISBN sold by ISBNdirect is a 979 number. Amazon handles them correctly. As of September 2026, the product page for a KDP paperback carrying a 979-8 ISBN shows an ASIN and an ISBN-13 and no ISBN-10 line at all, while a 978 title still shows both. That is not a missing field.
Some do. The Book Industry Study Group noted in November 2022 that some systems "continue to rely on or convert 13-digit ISBNs to 10-digit identifiers". Handle it like this.
If your ISBN starts with 978, convert it and enter the 10-digit form. Nothing is lost, because the two are the same identifier.
If your ISBN starts with 979, there is no correct 10-digit answer. Do not invent one, and do not let a tool invent one for you. Enter the 13-digit number in the ISBN field if the form accepts it, leave the ISBN-10 field blank, and if the form refuses, tell the operator that 979 ISBNs have had no 10-digit form since 2020. The International ISBN Agency's instruction to the trade is that ISBNs are "recorded in all systems and communicated to partners ONLY in their complete 13-digit form", so the fix belongs on their side. On Amazon, searching the 13-digit number or the ASIN finds the book. IngramSpark says it distributes 979 titles to all its partners.
Either way, print the barcode from the 13-digit number. A book barcode is an EAN-13, so an ISBN-10 barcode does not exist, and our barcode generator works from the 13-digit form.
Find the number on your copyright page or above the barcode and run it through the validator to confirm it is intact. If it has 10 digits, convert it and use the 13-digit form from now on in your metadata, your retailer accounts and your press material. If you are publishing a new edition or format, it needs an ISBN of its own, and our guide to getting an ISBN as a self-published author covers where to buy one and what the free KDP and IngramSpark numbers cost you in return.
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