ISBN Decoder & Validator
Paste any ISBN-10 or ISBN-13 to instantly decode its components — registration group, publisher prefix, publication number, and check digit.
Hyphens and spaces are ignored. Accepts ISBN-10 or ISBN-13.
ISBN Registration Groups
View all groups →Each ISBN begins with a registration group that identifies the country or language area. There are approximately 160 active groups worldwide.
Major Publishers
Browse all publishers →Every publisher that uses the ISBN system is assigned a unique registrant prefix. Below are some of the largest publishers by ISBN volume.
What is an ISBN?
An ISBN (International Standard Book Number) is a unique numeric identifier assigned to every commercially published book. The standard is defined by ISO 2108 and administered by the International ISBN Agency, with national agencies in each participating country.
Every ISBN encodes four pieces of information: the registration group (a country or language area), the registrant (the publisher), the publication number (the specific title/edition), and a check digit for error detection. This decoder unpacks all four components from any ISBN you enter.
ISBN-10 vs ISBN-13
Since January 1, 2007, all new ISBNs are issued in the 13-digit format (ISBN-13), which is identical to the EAN-13 barcode used in retail. Older books carry a 10-digit ISBN-10. The two are interconvertible for books in the 978-prefix range: strip the leading "978" and recalculate the check digit.
Books assigned under the newer 979- prefix have no ISBN-10 equivalent.
Full comparison guide →How to Read an ISBN
An ISBN-13 has five distinct parts separated by hyphens:
This ISBN (978-0-596-51774-8) is an O'Reilly book. Group 0 = English language; publisher 596 = O'Reilly Media.
What Does the Check Digit Do?
The last digit of every ISBN is a check digit computed from the preceding digits using a weighted sum algorithm. For ISBN-13, this uses the EAN-13 MOD-10 algorithm (alternating weights of 1 and 3). For ISBN-10, it uses MOD-11 (weights 10 down to 1, with X representing 10).
If a single digit is transcribed incorrectly, or two adjacent digits are transposed, the check digit catches it. This decoder verifies the checksum for every ISBN you enter.
How the check digit algorithm works →ISBN Guides
How the two formats differ, why ISBN-13 replaced ISBN-10, and how to convert between them.
Step-by-step walkthrough of the MOD-11 (ISBN-10) and MOD-10 (ISBN-13) algorithms with worked examples.
What each segment of an ISBN means and how to identify the country, publisher, and edition.
Why 979 was introduced, which books use it, and why 979-ISBNs have no ISBN-10 equivalent.
How to obtain an ISBN as a self-publisher, what prefix you'll receive, and when you need one.
Browse all ~160 ISBN registration groups by country and language area.