ISBN Validator

Check that an ISBN-10 or ISBN-13 is valid, and see the check digit calculation step by step. Free, no signup needed.

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Frequently Asked Questions

ISBN-13 is the current standard for book identification, consisting of 13 digits that uniquely identify a book edition.

For an ISBN-13, the last digit is calculated using a specific algorithm that alternates multiplying digits by 1 and 3, ensuring the ISBN is mathematically valid.

Common issues include incorrect length (an ISBN has 10 or 13 digits), wrong prefix (an ISBN-13 must start with 978 or 979), or an incorrect check digit.

You can enter ISBNs with or without hyphens, spaces, or other characters. We'll automatically extract just the digits (plus a final X on an ISBN-10).

Yes. Enter all 10 characters and the tool checks it with the ISBN-10 rule: the first nine digits are multiplied by 10 down to 2, and the check digit comes from the remainder after dividing by 11. A check digit of 10 is written as X.

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How ISBN-13 Validation Works

ISBN-13 uses a mathematical algorithm to verify the number is correct. The last digit (check digit) is calculated from the first 12 digits using a specific formula.

The validation process:

1
Check that the ISBN has exactly 13 digits
2
Verify it starts with 978 or 979 (valid prefixes)
3
Multiply each of the first 12 digits by 1 or 3 (alternating)
4
Sum all results and calculate the check digit
5
Compare calculated digit with the entered digit

Examples: See how the validation algorithm works:

Understanding ISBN-13 Structure

ISBN-13 is a 13-digit identifier where each section has a specific purpose. Understanding this structure helps you recognize valid ISBNs and understand how validation works.

979-8-89123-456-7
979
EAN prefix - Identifies this as a book
8
Registration group - 8 = United States
89123
Publisher identifier - Assigned to publisher
456
Title identifier - Specific to this book
7
Check digit - Calculated from other digits

Older ISBN-10 numbers:

ISBN-10, the format used before 2007, is the same number without the 978 prefix and with a different check digit: multiply the first 9 digits by 10 down to 2, add them up, and the check digit makes the total divisible by 11 (10 is written as X). ISBNs that start with 979, like the example above, have no ISBN-10.