ISBN Validator

An International Standard Book Number (ISBN) is a unique numeric identifier assigned to books and book-like products. It helps publishers, libraries, booksellers, and readers reliably identify and order specific editions of a book.

ISBN-10 vs ISBN-13

• ISBN-10: Used before 2007. 10 digits, last digit may be X (representing 10). Uses a weighted modulo-11 checksum.
• ISBN-13: Current standard since January 2007. 13 digits, always numeric. Uses the same EAN-13 checksum algorithm (weighted modulo-10).

How Check Digits Work

ISBN-10: Multiply each of the first 9 digits by its position weight (10, 9, 8, ..., 2), sum them, then compute (11 - sum mod 11) mod 11. If the result is 10, the check digit is X.

ISBN-13: Multiply each of the first 12 digits alternately by 1 and 3, sum them, then compute (10 - sum mod 10) mod 10.

Converting ISBN-10 to ISBN-13

Prepend "978" to the first 9 digits of the ISBN-10 (dropping the old check digit), then recalculate the check digit using the ISBN-13 algorithm.