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How to use ISBN Validator & Check Digit

Enter an ISBN-10 or ISBN-13, and the tool validates it and computes the correct check digit.

Frequently asked questions

What is an ISBN check digit?

The last digit of an ISBN is a checksum. ISBN-10 uses a weighted mod-11 sum (with 'X' meaning 10); ISBN-13 uses an alternating 1/3 weighted mod-10 sum.

Can this convert ISBN-10 to ISBN-13?

This tool validates and computes check digits. An ISBN-10 becomes ISBN-13 by prefixing '978' and recomputing the final check digit, which the ISBN-13 mode will do for you.

Are hyphens required?

No — hyphens and spaces are ignored. Only the digits (and a trailing X for ISBN-10) are used in the calculation.

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