ISBN Validator & Converter

Validate ISBN-10 and ISBN-13 numbers, fix the check digit and convert between ISBN-10 and ISBN-13.

How do I check if an ISBN is valid?

Paste one or more ISBNs (with or without hyphens). The validator recalculates the check digit — mod 11 for ISBN-10, where X means 10, and mod 10 for ISBN-13 — tells you whether each number is valid, shows the correct check digit if not, and converts between ISBN-10 and ISBN-13.

ISBN-10 vs ISBN-13

Since 2007 books use 13-digit ISBNs starting with 978 or 979. Every ISBN-10 has a 978 ISBN-13 equivalent; ISBN-13s starting with 979 have no ISBN-10 form.

Common errors

A typo in one digit — the check digit catches it.
Two swapped digits — also detected by the ISBN-10 check.
Using a barcode add-on (price code) as part of the ISBN.

Frequently asked questions

Does a valid ISBN mean the book exists?

No, it only means the number is correctly formed.

Can I check many ISBNs?

Yes, up to 500 at once, and copy the converted column.

Is it free?

Yes.