ISBN Validator & Converter
Validate ISBN-10 and ISBN-13 checksums with auto-detection, plus convert between the two formats.
How this tool works
Enter an ISBN
ISBN-10 or ISBN-13, with or without hyphens - the format is detected automatically by length.
The check digit is validated
Using the correct algorithm for the detected format - weighted-sum for ISBN-10, alternating 1-3 for ISBN-13.
See exactly what failed
An invalid character position or a checksum mismatch is identified specifically, not just flagged as "invalid."
Get the equivalent format
A valid ISBN converts automatically to its ISBN-10 or ISBN-13 counterpart, when one exists.
Quick facts
- Category
- Validators
- Best for
- Verifying a book's ISBN before entering it into a catalog or database
About this tool
Enter an ISBN and this tool automatically detects whether it's the older 10-digit or current 13-digit format based on length, then validates its check digit using the correct algorithm for that format - ISBN-10 uses a weighted sum with an "X" representing 10 in the final position, while ISBN-13 uses the same alternating 1-3 weighting as a UPC/EAN barcode, since ISBN-13 was specifically designed to be barcode-compatible. When validation fails, the tool identifies whether the problem is an invalid character at a specific position or a checksum mismatch, rather than just reporting "invalid" - a check digit that doesn't match its expected value usually means a single mistyped digit somewhere in the number. As a bonus, a valid ISBN-10 is automatically converted to its ISBN-13 equivalent (by prefixing "978" and recomputing the check digit) and vice versa, when the conversion is possible - not every ISBN-13 has an ISBN-10 equivalent, since only the "978" prefix range maps back to the original 10-digit system. Useful for verifying a book's ISBN before entering it into a catalog, or converting between formats when a system expects one or the other. Runs entirely client-side.
Why use this tool
Auto-detects the format
No need to specify ISBN-10 vs ISBN-13 - the correct validation algorithm is chosen automatically.
Specific failure diagnosis
Distinguishes an invalid character from a checksum mismatch instead of a generic error.
Built-in format conversion
Get the ISBN-10 or ISBN-13 equivalent of a valid ISBN without a separate conversion step.
Handles the "X" check digit
Correctly treats an "X" as the value 10 in ISBN-10's final position, per the actual standard.
Frequently asked questions
ISBN-10's check digit algorithm can produce a computed value of 10, but a single digit can only represent 0-9 - the standard resolves this by using the letter "X" to represent that value of 10 in the final position. It's a valid, standard part of the format, not an error, and this tool handles it correctly on both validation and generation.
ISBN-13 was introduced as an extension of the existing 10-digit system by adding a "978" prefix (and later "979" for expanded capacity as the 978 range filled up), making it compatible with EAN/UPC barcodes. Only ISBNs in the "978" range map back to a valid 10-digit ISBN, since that's the range that originally was the 10-digit system; a "979"-prefixed ISBN-13 has no ISBN-10 equivalent because no such book ever existed in the older format.
It almost always means a single digit was mistyped somewhere in the number - both ISBN-10 and ISBN-13's check digit is mathematically derived from the other digits, so any transposition or typo in those digits, or in the check digit itself, will cause the computed checksum not to match. Double-check the number against its original source (like the book's copyright page or back cover) rather than assuming the tool is wrong.
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