ISBN-13 with Checksum Validator

ISBN-13: the book barcode and its mod-10 check digit

The ISBN-13 (International Standard Book Number) is the 13-digit identifier printed on every commercially published book, defined by ISO 2108 and administered by the International ISBN Agency. Since 1 January 2007 all ISBNs are 13 digits — the old 10-digit form was migrated by prefixing 978 and recomputing the check digit. The validator on this page verifies the structure and, crucially, the check digit.

An ISBN-13 is physically a GTIN-13 / EAN-13 barcode, so it shares the EAN check-digit algorithm: multiply the first 12 digits alternately by 1 and 3, sum them, and the check digit is (10 − (sum mod 10)) mod 10.

The five parts of 978-0-306-40615-7

• Prefix (978 or 979): the GS1 "Bookland" prefix that makes a book scan like any retail product.
• Registration group (0): language/region area — 0 and 1 are English; 85 is Brazil, 972 Portugal.
• Registrant (306): the publisher, assigned by the national agency.
• Publication (40615): the specific title/edition.
• Check digit (7): the mod-10 digit computed above.

Where it shows up

• Retail & libraries: point-of-sale scanning, cataloguing (MARC records), inter-library loan.
• Distribution: Amazon, Ingram, Nielsen BookData and national bibliographies all key off the ISBN.
• Metadata: ONIX feeds, the barcode under the back-cover EAN.
• Mock data / testing: generating checksum-valid ISBNs for catalog fixtures.

Common pitfalls

• Hyphens are cosmetic: the group/registrant boundaries vary in length, so strip hyphens before validating, then re-hyphenate using the agency's ranges if you need a pretty form.
• 979 has no 10-digit form: 979-prefixed ISBNs (including all former ISMN music) cannot be converted back to ISBN-10.
• Check digit can be 0–9: unlike ISBN-10, the ISBN-13 check digit is never X.
• Valid checksum ≠ assigned: passing the algorithm doesn't mean a real book exists at that number.

FAQ

How is the check digit computed? Weights 1,3,1,3… over the first 12 digits; check = (10 − sum mod 10) mod 10. A different algorithm from ISBN-10's mod-11.

Can I convert ISBN-10 to ISBN-13? Yes: drop the ISBN-10 check digit, prefix 978, recompute the mod-10 check digit. The reverse only works for 978 numbers.

Is an ISBN the same as the barcode? The EAN-13 barcode on a book is the ISBN-13; the price/currency may be encoded in a separate add-on barcode beside it.