ISBN Validator
Validate ISBN-10 and ISBN-13 book identifiers with check digit verification and format conversion. Perfect for publishers, libraries, and book collectors.
Enter an ISBN-10 (10 digits) or ISBN-13 (13 digits). Hyphens and spaces are optional.
ISBN Format Examples
ISBN-1010-Digit Format
0-306-40615-20306406152043942089XISBN-1313-Digit Format
978-0-306-40615-79780306406157979-1-234-56789-0Note: The hyphen positions shown are simplified. Actual ISBN formatting varies by publisher and registration group. Our validator accepts ISBNs with or without hyphens.
Check Digit Validation
Verify ISBN integrity using industry-standard algorithms
Format Conversion
Automatically convert ISBN-10 to ISBN-13 format
Flexible Input
Accepts ISBNs with or without hyphens and spaces
How ISBN Validation Works
ISBN-10 Check Digit Algorithm
Multiply each digit by its position
The first digit is multiplied by 10, second by 9, third by 8, and so on down to the ninth digit multiplied by 2.
Calculate the sum modulo 11
Add all the products together and find the remainder when divided by 11.
Determine check digit
Subtract the result from 11. If the result is 10, use 'X'; if 11, use '0'.
ISBN-13 Check Digit Algorithm
Apply alternating weights
Multiply odd-position digits (1st, 3rd, 5th, etc.) by 1 and even-position digits by 3.
Sum and calculate modulo 10
Add all products for the first 12 digits and find the remainder when divided by 10.
Determine check digit
Subtract the result from 10. If the result is 10, use 0 as the check digit.
Frequently Asked Questions
What is an ISBN?
ISBN (International Standard Book Number) is a unique numeric commercial book identifier. ISBN-10 uses 10 digits while ISBN-13 uses 13 digits. The last digit is a check digit used to validate the ISBN and detect errors in entry or transmission.
What is the difference between ISBN-10 and ISBN-13?
ISBN-10 is the older format with 10 digits, while ISBN-13 is the newer format with 13 digits that prepends '978' or '979' to the ISBN-10 number. Since January 1, 2007, all new ISBNs are assigned in the 13-digit format to accommodate the growing number of publications.
How is the check digit calculated?
For ISBN-10: multiply each of the first 9 digits by its position (10 to 2), sum them, find modulo 11, and subtract from 11. For ISBN-13: apply alternating weights of 1 and 3 to the first 12 digits, sum them, find modulo 10, and subtract from 10. The check digit helps detect transcription errors.
Can I convert ISBN-10 to ISBN-13?
Yes! Our validator automatically converts valid ISBN-10 numbers to ISBN-13 format by prepending '978' to the first 9 digits and recalculating the check digit using the ISBN-13 algorithm. This is useful for updating old book records to the current standard.
What does the check digit validate?
The check digit validates that the ISBN was entered correctly and detects common errors like transposed digits or incorrect numbers. It uses mathematical algorithms (modulus 11 for ISBN-10, modulus 10 for ISBN-13) to verify the number's integrity, but it doesn't verify that the ISBN is actually assigned to a book.
Why do some ISBN-10s end with 'X'?
In ISBN-10, the check digit can be 0-9 or X. When the calculated check digit is 10, it's represented as 'X' (the Roman numeral for 10) since the check digit must be a single character. This is unique to ISBN-10; ISBN-13 only uses digits 0-9.