ISBN Validator

ISBN Validator

ISBN Validator checks ISBN-10 and ISBN-13 numbers, formats them with hyphens, and converts between the two.

How to use it

1. Enter an ISBN. Hyphens and spaces are ignored.
2. Read whether the check digit is valid.
3. Copy the formatted or converted version.

Two checksum schemes

ISBN-10 multiplies each digit by a descending weight from 10 down to 1 and requires the total to divide evenly by 11. Because the check value can be ten, ISBN-10 uses the letter X for that case, which is why some ISBNs end in a letter.

ISBN-13 alternates weights of 1 and 3 and requires the total to divide by 10, the same scheme used by EAN barcodes. Converting a 10 to a 13 means dropping the old check digit, prefixing 978, and recomputing, which is why the two forms of the same book differ in more than just length.

When it helps

• Checking an ISBN before ordering or cataloguing a book.
• Converting between the 10 and 13 digit forms.
• Catching a transcription error from a printed page.
• Formatting an ISBN correctly with hyphens.

Common mistakes

• Treating the X as an error. In ISBN-10 it is a legitimate check digit meaning ten.
• Assuming a valid ISBN means the book exists. The checksum only proves internal consistency.
• Expecting hyphen positions to be uniform. They vary by registration group and publisher, and are not fixed.