ISBN converter and validator
Convert between ISBN-10 and ISBN-13, check a check digit, and see which registration group issued it. Runs entirely in your browser.
How the check digit works
The last character of an ISBN is not part of the identifier. It is a checksum over the others, chosen so that a single mistyped digit — or two adjacent digits swapped, the most common human error — produces an invalid number rather than a different valid book.
ISBN-13
Multiply the twelve digits alternately by 1 and 3, sum them, and the check digit is whatever makes the total a multiple of 10.
9·1 + 7·3 + 8·1 + 0·3 + 2·1 + 2·3 + 6·1 + 4·3 + 5·1 + 8·3 + 1·1 + 1·3 = 127
127 + 3 = 130, a multiple of 10 → check digit 3
ISBN-10
Multiply the nine digits by 10, 9, 8 … 2, sum them, and the check digit makes the total a multiple of 11. Eleven possible remainders and only ten digits is why ISBN-10 has the letter X: it stands for a check value of ten.
That is why an ISBN can contain a letter. X appears only as the final character of an ISBN-10, never in an ISBN-13, whose modulus is 10.
Converting between them
To go from ISBN-10 to ISBN-13: discard the ISBN-10 check digit, prefix 978,
and recompute the check digit under the mod-10 rule. The nine identifying digits never
change, which is why the two forms are the same book and cite identically.
The conversion that does not exist
An ISBN-13 beginning 979 has no ISBN-10 form at all. ISBN-10 was only ever a 978-space identifier; the 979 prefix was opened when 978 began to fill, and there is no nine-digit number to map it back to.
979-8 is the block Amazon's Kindle Direct Publishing issues from, and it holds
millions of titles, so code that assumes every ISBN has a ten-digit form now fails on a large
share of recent books. If you are storing ISBNs, store the 13.
Registration groups
The digits after the prefix identify the registration group — a language area or country,
not a publisher. They are variable length, which is why this cannot be read off by position:
978-0 is one digit, 978-612 is three.
| Group | Area |
|---|---|
| 978-0, 978-1 | English language |
| 978-2 | French language |
| 978-3 | German language |
| 978-4 | Japan |
| 978-5 | Russian language |
| 978-7 | China |
| 979-8 | United States — largely self-published |
| 979-10 | France |
| 979-12 | Italy |
A group says where the identifier was issued, not where a book was written, printed or sold.
Cite one
Enter an ISBN on the home page for a formatted citation in five styles, or read how to cite a book.