ISBN Validator
Enter an ISBN-10 or ISBN-13 to check its check digit. If it is a valid ISBN-10, the tool also shows its ISBN-13 equivalent. Hyphens and spaces are ignored.
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How It Works
An ISBN carries a check digit in its last position, calculated from the digits before it, so a single wrong or swapped digit almost always breaks the maths and gives the mistake away. There are two formats. ISBN-10 was used until 2006, and ISBN-13 has been standard since 2007 and doubles as the book's barcode.
For an ISBN-10, each of the ten characters is multiplied by a weight that counts down from 10 to 1, and the results are added together. A final check character of X stands for the value 10. The number is valid when that sum divides evenly by 11. For an ISBN-13, the thirteen digits are multiplied alternately by 1 and 3, starting with 1, and the number is valid when that sum divides evenly by 10. Converting an ISBN-10 to ISBN-13 keeps the first nine digits, adds 978 at the front, and recomputes the check digit under the ISBN-13 rule.
Worked Example
Take the sample number 978-1-23456-789-7, which is made up rather than a real book. Reading the thirteen digits and multiplying alternately by 1 and 3 gives 9, 21, 8, 3, 2, 9, 4, 15, 6, 21, 8, 27, and 7. Those add up to 140, which divides evenly by 10, so the check digit is correct and the number is a valid ISBN-13.
When You Would Use This
Anyone working with book data runs into ISBNs that need checking: a bookseller loading a catalogue, a librarian cleaning up records, or a self-publisher confirming the number on a cover proof. A quick check digit test catches a transcription error before it ends up in a database, and the ISBN-10 to ISBN-13 conversion saves a fiddly manual recalculation when older records only hold the ten-digit form.
Frequently Asked Questions
What is the difference between ISBN-10 and ISBN-13?
ISBN-10 is the older ten-character format used until the end of 2006. ISBN-13 is the current thirteen-digit format, which is also a valid EAN-13 barcode. Every ISBN-10 has a direct ISBN-13 equivalent that starts with 978.
What does the X at the end of an ISBN-10 mean?
The ISBN-10 check digit can be any value from 0 to 10. Since 10 will not fit in a single digit, it is written as the letter X. It can only ever appear in the last position, never anywhere else in the number.
How is the check digit worked out?
For ISBN-10, each digit is multiplied by a weight from 10 down to 1, the results are added, and a valid number is divisible by 11. For ISBN-13, the digits are multiplied alternately by 1 and 3, and a valid total is divisible by 10.
Can I convert an old ISBN-10 to ISBN-13?
Yes. When you enter a valid ISBN-10, the tool shows its ISBN-13 form. It keeps the first nine digits, puts 978 in front, and recalculates the final check digit for the new thirteen-digit number. This is a common need when updating older catalogue data.
Does a valid ISBN mean the book exists?
No. The check only proves the number is internally consistent. A number can pass the check digit test and still not have been assigned to any published book. To confirm a title, look the ISBN up in a library or bookseller catalogue.
Do the hyphens and spaces matter?
No. The groups in an ISBN, such as the language and publisher parts, are separated by hyphens purely for readability. The tool removes hyphens and spaces before checking, so 978-0-306-40615-7 and 9780306406157 are treated the same.