Validate an ISBN
Examples
ISBN Checker validates and formats ISBN-10 and ISBN-13 numbers for books. Enter any ISBN — with or without dashes or spaces — to verify its check digit, convert between ISBN-10 and ISBN-13, and see the publisher prefix and registration group. Also fetches book metadata from the Open Library API: title, author, publisher, and publication year when available.
ISBN (International Standard Book Number) is a numeric commercial book identifier. ISBN-10 (9-digit base number + 1 check digit, used before 2007): check digit is calculated using modulo 11 (the check digit can be 0-9 or X for 10). ISBN-13 (12 digits + 1 check digit, current standard since 2007): based on EAN-13 barcode format, check digit calculated using modulo 10 alternating weights 1 and 3. All ISBNs beginning with 978 are books; 979-10 is a newer French publisher prefix.
ISBN structure (ISBN-13): prefix element (978 or 979) + registration group (country/language, 1-5 digits) + publisher (varies) + publication (varies) + check digit. Groups: 0 and 1 are English-language, 2 is French, 3 is German, 4 is Japan, 7 is China, 88 is Italy, etc. The group and publisher lengths vary — the ISBN Agency maintains the range tables that determine where publisher and title elements split.
Validate ISBN-13
Result: 978-0-306-40615-7 → Check digit: 7 ✓ Valid → Group: 0 (English), Publisher: 306
Convert ISBN-10 to ISBN-13
Result: 0-306-40615-2 → 978-0-306-40615-7
Check digit formula
Result: ISBN-13: sum alternating ×1/×3 → total mod 10 → check = (10 - remainder) mod 10
How is the ISBN-13 check digit calculated?
ISBN-13 check digit calculation: (1) Take the first 12 digits. (2) Multiply alternating digits by 1 and 3 (positions 1,3,5,7,9,11 × 1; positions 2,4,6,8,10,12 × 3). (3) Sum all products. (4) Take modulo 10 of the sum. (5) Check digit = (10 - remainder) % 10. If remainder is 0, check digit is 0. Example: 978030640615x — sum: 9×1+7×3+8×1+0×3+3×1+0×3+6×1+0×3+6×1+1×3+5×1+7×3 = 9+21+8+0+3+0+6+0+6+3+5+21 = 82. 82 mod 10 = 2. (10-2)%10 = 8... wait, let me recalculate: for 9780306406157, the check digit is 7.
What is the difference between ISBN-10 and ISBN-13?
ISBN-10: used before January 1, 2007. 10 digits (9 base + 1 check). Check digit modulo 11 — can be 0-9 or X (=10). First digit is the registration group. ISBN-13: current standard since 2007. 13 digits (12 base + 1 check). EAN-13 barcode compatible. Starts with 978 (or newer 979). Check digit modulo 10. Every ISBN-10 has an equivalent ISBN-13 (add 978 prefix and recalculate check digit). ISBN-13 starting with 979 have no ISBN-10 equivalent.
What does the ISBN registration group tell you?
The registration group identifies the language/country of the publisher. Group 0 and 1: English-language publishers (US, UK, Australia, Canada, etc.). Group 2: French. Group 3: German. Group 4: Japan. Group 5: Russia and former Soviet states. Group 7: China. Group 88: Italy. Group 89: Korea. Group 956: Chile. Group 99977: Laos. The group is identified by range tables maintained by the International ISBN Agency (isbn-international.org). The ranges are not simply decoded by the first digit — multiple groups share the same prefix and are disambiguated by longer prefixes.
Where can I get an ISBN for my book?
In the US: Bowker is the official ISBN agency — purchase ISBNs at myidentifiers.com. A single ISBN costs around $125, a block of 10 costs ~$295. Each format (hardcover, paperback, ebook, audiobook) needs its own ISBN. Self-publishing platforms: Amazon KDP, IngramSpark, and Lulu offer free ISBNs for books published on their platforms — but those ISBNs are owned by the platform, not you. For full ownership and broader distribution, purchase your own ISBNs from Bowker. Other countries have their own ISBN agencies (the International ISBN Agency directory lists them all).
Can I look up a book by its ISBN?
Yes — several public APIs and databases: Open Library (openlibrary.org) — free, extensive coverage, API: https://openlibrary.org/api/books?bibkeys=ISBN:9780306406157&format=json. Google Books API — includes cover images and preview links. WorldCat (OCLC) — library union catalog. Goodreads API (deprecated). Amazon product API (requires developer account). These can be used to build book lookup features, verify ISBNs, and retrieve metadata (title, author, publisher, year, description, cover image).