ISBN validator — check ISBN-10 and ISBN-13 and convert between them

How to use the ISBN validator

1. Type or paste an ISBN into ISBN-10 or ISBN-13 (or 9 / 12 digits for the check digit). Hyphens and spaces are fine.
2. For a full 10- or 13-character ISBN, read Result, Type and Check digit expected. A valid number also shows its other form.
3. For 9 digits, the tool returns the ISBN-10 Check digit and the complete ISBN-10. For 12 digits, it returns the ISBN-13 check digit and the complete ISBN-13.

What it does and when to use it

Every ISBN ends with a check digit that catches most copying mistakes. Libraries, booksellers, self-publishers and developers who import book lists use this to spot a mistyped number before it reaches a catalogue or an order. The conversion is useful when an older system only takes ISBN-10, or a newer one only takes ISBN-13.

To create sample numbers for testing, use the ISBN-13 generator or the ISBN-10 generator. For card and IMEI numbers, which use a different check, see the Luhn validator.

How it works

ISBN-10. Multiply the first nine digits by 10, 9, 8 and so on down to 2, and add the results. The check digit is (11 − sum mod 11) mod 11, with 10 written as X.

ISBN-13. Starting from the right of the first twelve digits, multiply by 3, 1, 3, 1 and so on, and add. The check digit is (10 − sum mod 10) mod 10.

Conversion. ISBN-10 to ISBN-13 adds the prefix 978 to the first nine digits and computes a new ISBN-13 check digit. The reverse works only for 978 numbers: drop the 978 and compute a new ISBN-10 check digit.

Worked examples

ISBN-13 to ISBN-10. 978-0-306-40615-7: the first twelve digits, weighted 1 and 3, add up to 93, and 10 − 3 = 7, so the number is valid. The tool shows Result: Valid, Type: ISBN-13 and As ISBN-10: 0306406152.

ISBN-10 to ISBN-13. 0-306-40615-2: the weighted sum is 0×10 + 3×9 + 0×8 + 6×7 + 4×6 + 0×5 + 6×4 + 1×3 + 5×2 = 130. 130 mod 11 is 9, and 11 − 9 = 2, which matches. The tool shows As ISBN-13: 9780306406157.

Check digit X. Entering the nine digits 080442957 gives a weighted sum of 199. 199 mod 11 is 1, and 11 − 1 = 10, so the tool returns Check digit: X and ISBN-10: 080442957X.

Limits and tips

• A wrong number shows Result: Invalid and the check digit it should have had, which usually points to the typo.
• Swapping two neighbouring digits is always caught in ISBN-10, but not always in ISBN-13. A 13-digit number that passes may still contain a swap.