ISBN Validator and Converter
Validate ISBN-10 and ISBN-13 numbers with the check-digit math shown step by step, convert between the two formats, compute a missing check digit, or bulk-check a whole list.
Type or paste an ISBN above to validate it instantly.
Check-digit math
Enter the first 9 digits of an ISBN-10 or the first 12 digits of an ISBN-13 to compute the missing check digit.
Frequently Asked Questions (FAQ)
How does this tool validate an ISBN-13 check digit?
An ISBN-13 is valid when the weighted sum of its 13 digits is a multiple of 10. The first 12 digits are multiplied alternately by 1 and 3, starting with 1, and the check digit is included in the sum. The tool shows every multiplication step so you can follow the exact math, for example 9x1 + 7x3 + 8x1 and so on.
How is an ISBN-10 check digit validated, and what does X mean?
An ISBN-10 is valid when the sum of its digits multiplied by the weights 10 down to 1 is a multiple of 11. Because the check digit can equal 10, it is written as the letter X in that position only. The tool accepts a lowercase or uppercase X as the final character and rejects it anywhere else.
Can every ISBN-13 be converted to an ISBN-10?
No. Only ISBN-13 numbers starting with the 978 prefix can be converted, because ISBN-10 numbers all map into that prefix range. ISBN-13 numbers starting with 979 have no ISBN-10 equivalent, and the tool tells you this instead of producing a wrong result. Conversion in the other direction, from ISBN-10 to ISBN-13, always works.
Why does the formatted output use generic spacing instead of official hyphens?
Official ISBN hyphenation splits the number by registration group, publisher range and title, and those ranges come from the official ISBN agency tables, which change over time. This tool shows a neutral, evenly spaced grouping for readability and never claims it is the official hyphenation, so it cannot mislead a publisher or printer.
Is my ISBN or ISBN list uploaded or stored anywhere?
No. Every check, conversion and bulk validation runs in your browser with JavaScript. Nothing you type is uploaded, stored or sent to any server.