Calculators
ISBN Checksum Calculator
Validate ISBN-10 and ISBN-13 checksums or generate missing check digits privately in your browser.
Enter 10 or 13 characters to validate an ISBN, or 9 or 12 digits to generate its check digit. Spaces and hyphens are ignored. ISBN-10 can end in X; ISBN-13 must start with 978 or 979. A valid checksum does not prove a book exists.
How ISBN check digits work
Enter a complete ISBN-10 (10 characters) or ISBN-13 (13 digits) to validate its checksum. Enter only the first 9 or 12 digits to generate the final check digit. Spaces and hyphens are removed; lowercase x is accepted as the final ISBN-10 check digit. Leading zeros are preserved. For ISBN-10, multiply the nine payload digits by weights 10 through 2; the check digit makes the total divisible by 11, with X representing 10. For ISBN-13, multiply the twelve payload digits by alternating weights 1 and 3; the check digit makes the total divisible by 10. ISBN-13 inputs must begin with 978 or 979. For payload 030640615 the check digit is 2, giving 0306406152. For payload 978030640615 the check digit is 7, giving 9780306406157. Invalid complete inputs show the expected digit without silently replacing the supplied digit. This tool checks checksum arithmetic and the ISBN-13 prefix; it does not verify publisher allocations, hyphen placement, book existence or registration. Input is limited to 100 characters including separators and stays entirely in your browser.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
How do I generate an ISBN check digit?
Enter nine digits for ISBN-10 or twelve digits for ISBN-13. For 978030640615, append the returned digit 7.
Why can ISBN-10 end in X?
The modulus-11 checksum can require the value ten, represented by X. ISBN-13 uses only decimal check digits.
Does a valid checksum prove the ISBN is registered?
No. This checks arithmetic and the ISBN-13 prefix only. It does not query book records or verify publisher allocations.
Can I paste hyphenated ISBNs?
Yes. Spaces and hyphens are ignored, leading zeros are preserved, and lowercase x is accepted. Hyphen placement is not validated.
Are ISBN-10 and ISBN-13 interchangeable here?
The calculator validates or generates within the input format. It does not convert between ISBN formats.