ISBN Validator

An ISBN (International Standard Book Number) is the unique identifier printed on almost every book published since 1970. This tool checks whether an ISBN is well-formed — that its final check digit actually matches the rest of the number — and converts a valid ISBN-10 into its modern ISBN-13 equivalent (and a 978-prefixed ISBN-13 back to ISBN-10). Paste a number with or without hyphens and spaces; everything runs in your browser, so nothing you enter is uploaded.

How to use it

Type or paste an ISBN into the input box. The tool automatically strips formatting characters, detects whether you gave it a 10- or 13-character ISBN, and shows a result table with the detected format, the check digit, the normalized number, and — when the ISBN is valid — its equivalent in the other format.

How the check digit works

Both ISBN formats end in a check digit derived from the preceding digits, which is what lets a validator catch typos and swapped characters.

ISBN-10

Each of the first nine digits is multiplied by a descending weight (10, 9, 8, … 2), and the tenth character is added with weight 1. The tenth character may be the letter X, which stands for the value 10. If the weighted total is divisible by 11, the ISBN-10 is valid.

ISBN-13

The thirteen digits alternate weights of 1 and 3, starting with 1. The check digit is chosen so the weighted total is divisible by 10. ISBN-13 numbers begin with a 978 or 979 EAN prefix, making them scannable as standard product barcodes.

Converting between formats

An ISBN-10 converts to ISBN-13 by prefixing 978 to its first nine digits and recomputing the ISBN-13 check digit. The reverse — ISBN-13 to ISBN-10 — is only possible for numbers in the original 978 range; 979-prefixed ISBNs have no ISBN-10 equivalent because that number space never existed under the old scheme.

The converted number is shown as plain digits, without hyphens. Correct hyphen grouping (prefix, registration group, registrant, and publication) depends on the ISBN registration-group range tables published by ISBN International, which cannot be derived from the number alone — so this tool deliberately avoids inventing groupings that could be wrong.

Is this the same as a barcode number?

Yes — a book's ISBN-13 is exactly the number encoded in its EAN-13 barcode, so scanning the barcode and reading the printed ISBN-13 should give the same digits.

Why did my ISBN fail validation?

The most common causes are a mistyped or transposed digit, a missing digit, or copying an ISBN-10 while including an unrelated stray character. A failed check digit means the number as entered cannot be a genuine ISBN.

Privacy

All validation and conversion happen locally in your browser. No ISBN is ever sent to a server.