About

The International Standard Book Number (ISBN) is a numeric commercial book identifier which is intended to be unique. Publishers purchase ISBNs from an affiliate of the International ISBN Agency. An ISBN is assigned to each separate edition and variation (except reprintings) of a publication.

Validity is determined not just by the length of the string, but by a mathematical checksum algorithm. ISBN-10 uses Modulo 11, while ISBN-13 uses Modulo 10 with alternating weights. This tool performs deep validation, verifying the structure against industry standards (ISO 2108), calculating the correct check digit if errors are found, and retrieving real-time book metadata.

Formulas

The validation logic relies on weighted modular arithmetic.

ISBN-10 Algorithm (Modulo 11)

For a 10-digit ISBN x, the checksum validity is defined by:

10∑i=1

11 − i⋅x_i ≡ 0 (mod 11)

Where x₁₀ can be 0-9 or X (10).

ISBN-13 Algorithm (Modulo 10)

For a 13-digit ISBN, weights alternate between 1 and 3:

13∑i=1

w_ix_i ≡ 0 (mod 10)

Where w_i = 1 if i is odd, and 3 if i is even.

Reference Data

Group Identifier	Region / Language	Example Prefix
0 & 1	English (UK, US, CA, AU, NZ)	978-0...
2	French Language	978-2...
3	German Language	978-3...
4	Japan	978-4...
5	Russian Federation	978-5...
7	China	978-7...
80 - 94	Various (e.g., 88 Italy, 84 Spain)	978-88...
600 - 649	Various (e.g., 607 Mexico)	978-607...
950 - 989	Various (e.g., 972 Portugal)	978-972...
9900 - 9989	Small Regions (e.g., 9946 Korea)	978-9946...

Frequently Asked Questions

ISBN-10 was the standard before 2007. ISBN-13 was introduced to expand capacity and align with the EAN-13 barcode system used for other retail products. ISBN-13s usually start with "978" or "979".

Yes. An ISBN-10 is converted by prepending the "978" prefix and recalculating the final check digit. However, ISBN-13s starting with "979" cannot be converted back to ISBN-10.

In ISBN-10, if the check digit calculation results in 10, the character "X" (Roman numeral for 10) is used to maintain a constant length of 10 characters.

Yes. If the ISBN is valid, the tool queries the OpenLibrary API to retrieve the book title, author, and cover image if available in their database.

Paste a list of ISBNs (one per line) into the bulk tab. The system will process each one individually, providing a validity report and conversion options for up to 1000 lines at once.