ISBN Validator & Converter

What this tool does

ISBN-10 uses a weighted checksum with weights 10 down to 1, where the final character can be the letter X to represent the value 10; the total must be a multiple of 11. ISBN-13 uses the same alternating 1-3 weighting as EAN-13 barcodes, and the total must be a multiple of 10. Since 2007 all new ISBNs are issued in the 13-digit form, made by prefixing 978 to the first nine digits of the ISBN-10 and recalculating the check digit, which is exactly what this tool's converter does.

How to use it

1. Enter a 10 or 13-character ISBN, with or without hyphens.
2. The tool detects whether it looks like an ISBN-10 or ISBN-13 and validates the check digit.
3. If it's a valid ISBN-10, its ISBN-13 equivalent appears automatically.

Privacy

This tool runs entirely in your browser. Your input is never uploaded, stored or shared — closing the tab removes it.

Frequently asked questions

Can this convert an ISBN-13 back to ISBN-10?

This tool focuses on the common ISBN-10 to ISBN-13 direction used by publishers since 2007; only ISBN-13s starting with the 978 prefix can be represented as ISBN-10 at all.

Why can ISBN-10 end in the letter X?

X represents the value 10 in the check digit position, since a single digit can't represent values above 9 and the checksum sometimes requires it.

Does this look up the book title?

No. It only validates and converts the number locally; no lookup is performed and nothing is sent anywhere.