ISBN Validator & Converter

Validate an ISBN-10 or ISBN-13 checksum (ISBN-10 uses mod-11 with an X check digit; ISBN-13 uses mod-10) and convert between the two. Runs entirely in your browser.

Mode

ISBN

Result

ISBN-10: weighted sum (d×10, d×9 … d×1) mod 11 = 0; the last digit may be X (value 10). ISBN-13: alternating 1/3 weights mod 10 = 0.