ISBN Validator and Converter

ISBN-10 is the older 10-digit format used until 2007; ISBN-13 is the 13-digit format used today, which is the same as the book's EAN-13 barcode. A 978-prefixed ISBN-13 maps directly to an ISBN-10, while a 979-prefixed one has no ISBN-10 equivalent. The two formats use different checksum formulas.

For ISBN-10 each of the first nine digits is multiplied by a weight from 10 down to 2, and the check digit makes the total a multiple of 11 (a value of 10 is written as X). For ISBN-13 the digits alternate weights of 1 and 3, and the check digit makes the total a multiple of 10.

An X only ever appears as the final check digit of an ISBN-10, where it stands for the value 10 that the mod 11 formula can produce. It is never a real digit and never appears in an ISBN-13.

The most common reasons are a mistyped digit, a wrong or missing check digit, or the wrong length (an ISBN must be exactly 10 or 13 digits after removing hyphens and spaces). A single transposed or wrong digit changes the checksum and fails validation.

Yes. When you enter a valid ISBN this tool shows both forms. An ISBN-10 becomes an ISBN-13 by prefixing 978 and recomputing the check digit, and a 978-prefixed ISBN-13 becomes an ISBN-10 by dropping the prefix and recomputing its check digit.

No. All validation and conversion happen locally in your browser, so the ISBN you paste never leaves your device.