Free tool
ISBN Converter & Validator
Paste any ISBN — with or without hyphens. Enter 9 or 12 digits to calculate the missing check digit.
ISBN-10 vs ISBN-13
The International Standard Book Number identifies a specific edition and format of a book. Ten-digit ISBNs were used from 1970; since January 2007 all new ISBNs are 13 digits. Every ISBN-10 has an ISBN-13 equivalent made by adding the prefix 978 and recalculating the last digit. ISBNs beginning with 979 have no ISBN-10 version.
How the check digit works
ISBN-10: multiply the digits by 10, 9, 8… down to 1 and add them up. The total must divide evenly by 11. If the check value works out to 10, it is written as X.
ISBN-13: multiply the digits alternately by 1 and 3 and add them up. The total must divide evenly by 10.
A failed check usually means a typo or a transposed pair of digits — this tool shows the digit the number should end with so you can spot the mistake. Learn more in ISBNs explained.