ISBN Validator (ISBN-10 & ISBN-13)
Check an ISBN-10's mod-11 checksum or an ISBN-13's alternating 1-3 weighted checksum, see which standard it is, and convert between the two.
Hyphens and spaces are ignored.
Check a list
Validate an ISBN
Paste a book number such as 978-0-306-40615-7 and this tool checks its checksum live and tells you whether it is a valid ISBN-10 or ISBN-13. Hyphens and spaces are stripped automatically, so you can copy the number in any common format without cleaning it up first. If the check digit does not match, you get a clear message so you can spot a typo before ordering, cataloguing, or entering the number into a system. For a valid ISBN it also shows the equivalent code in the other standard, converting ISBN-10 to ISBN-13 and back so you can normalise old and new records, and prints both hyphenated as they appear on a book — split into prefix, group, registrant, publication and check digit by the International ISBN Agency's range table — each with its own Copy button.
How the checksum works
An ISBN-10 uses a weighted mod-11 checksum: each of the first nine digits is multiplied by weights 10 down to 2, the check digit closes the sum, and the total must be divisible by 11. Because a remainder can equal 10, ISBN-10 allows the letter X as its final check digit. An ISBN-13 instead alternates weights of 1 and 3 across its thirteen digits and must be divisible by 10. This tool applies both rules exactly, so a number only reads as valid when its check digit is correct. An ISBN-13 must also start with 978 or 979: a thirteen-digit barcode whose checksum works but whose prefix is anything else (977 is an ISSN, for periodicals) is refused as not a book number.
Frequently asked questions
What is the difference between ISBN-10 and ISBN-13?
ISBN-10 is the older 10-digit format using a mod-11 checksum that can end in the letter X. ISBN-13 is the current 13-digit format (starting 978 or 979) with a mod-10 checksum. This tool detects and validates both automatically.
Why is my ISBN showing as invalid?
The most common cause is a mistyped digit, which breaks the checksum. Make sure you have exactly 10 or 13 digits (an X is only allowed as the last digit of an ISBN-10) and that no digits were dropped or transposed when copying.
Does it say what is wrong with an invalid ISBN?
The page says which check failed: a character that does not belong, the wrong length, or the check digit — and for the check digit it shows the digit expected beside the one you typed.
Can it hyphenate an ISBN the way it is printed on a book?
Yes. For a valid ISBN the page adds a “Hyphenated, as printed on a book” block: the ISBN-13, and the ISBN-10 where there is one, with their hyphens and a copy button each, and the parts named — prefix, group, registrant, publication and check digit. The hyphens are placed by the International ISBN Agency’s range table, because the parts have no fixed lengths; a valid number in a range the Agency has not assigned gets a sentence saying so rather than an invented split.
Can it check a whole list of ISBNs, or finish a number that is missing its check digit?
Yes. Open “Check a list” and paste the ISBNs one per line: the page counts how many are valid and how many are not, and shows a table of line, ISBN, type and result, giving each refused number the same reason the single box would. Copy results hands over each row’s ISBN, type and result as tab-separated text, ready for a spreadsheet. In the single box, a number typed without its last digit still gets the length message, and under it the check digit and the finished ISBN, with a Copy completed ISBN button. The longer form is finished only when it starts with a prefix reserved for books.