ISBN checker
Check an ISBN-10 or ISBN-13 checksum, calculate a missing check digit, or convert between equivalent ISBN formats.
One identifier, up to 128 characters. ASCII digits, spaces, hyphens and a final ISBN-10 X are supported. No book database, publisher-range lookup or ownership check is performed. Calculation does not allocate an ISBN. Runs on your device. Enter one ISBN with optional spaces or hyphens. For Calculate check digit, omit the final check character. Up to 128 characters. Results update as you type. Up to 128 characters.
Your result
How to use ISBN checker
- Choose Check ISBN or Calculate check digit.
- Enter one complete ISBN, or its 9- or 12-digit body for check-digit calculation.
- Review format, checksum and any available conversion, then download the JSON report.
Useful next steps
Check an ISBN without looking up a book
Enter one ISBN with or without spaces and hyphens. The checker accepts lowercase x as the final ISBN-10 check character. It reports format and checksum separately, so a number with the right length can still fail its check. A matching checksum does not prove that a publisher was allocated the number or that a book exists.
Calculate a missing check digit
Choose Calculate check digit and enter the body without the final character: 9 digits for ISBN-10 or 12 digits for ISBN-13. The result supplies the check character and explains that assignment has not been verified. For a complete ISBN with a wrong checksum, the tool shows the expected character but does not silently fix or convert the number.
Convert only where an equivalent exists
A checksum-valid ISBN-10 can be expressed as a 978 ISBN-13 with a recalculated final digit. A valid 978 ISBN-13 can convert back. ISBNs beginning with 979 have no ISBN-10 equivalent. The 979-0 prefix belongs to music identifiers and is rejected here. Publisher ranges and the placement of hyphens are not checked.