ISBN Converter (10 to 13 digits)

An ISBN identifies a book. Numbers assigned on or after 1 January 2007 have 13 digits (ISBN-13); earlier ones had 10 (ISBN-10). An ISBN-13 is an ISBN-10 with the prefix 978 in front and the check digit recomputed. So an ISBN-13 beginning with 978 can be converted back, while one beginning with 979 has no ISBN-10 equivalent.

For ISBN-10, multiply the digits by weights 10, 9, 8 ... 2 from the left, sum them, then take (11 - sum mod 11) mod 11. Only this value can be 10, which is written as X. For ISBN-13, multiply by alternating weights 1 and 3 from the left, sum them, then take (10 - sum mod 10) mod 10. The weights and the modulus differ, so using the wrong length always gives a mismatch.

The hyphens separate the prefix, the registration group, the registrant, the publication, and the check digit. Their positions depend on the length of the registrant element, so they cannot be derived from the digits alone. This tool ignores hyphens in the input and prints the result as plain digits. The correct split cannot be derived from the digits alone, so no hyphenation is invented.

The value you type is never sent to a server. The JavaScript loaded with the page does the calculation locally.

The ISBN-10 check digit comes from a modulo 11 calculation, so it can take 11 values from 0 to 10. Ten cannot be written as a single digit, so X (the Roman numeral for ten) is used. X appears only in the final position and never elsewhere.

ISBN-10 had no prefix element. ISBN-13 was designed so that adding 978 reproduces the old numbers. The prefix 979 was introduced only after the move to 13 digits, so no corresponding 10-digit number ever existed and no conversion is possible.

Either the number was copied incorrectly or it is genuinely invalid. Common causes are confusing 0 with O or 1 with l, and transposed digits. This tool also shows the correct check digit, so if only the last digit differs, a copying error is the likely cause.

No. The calculation happens entirely in your browser and no request is made, so unpublished bibliographic data stays on your machine.