📚 ISBN-10 ↔ ISBN-13 Converter & Validator
Paste an ISBN to verify its check digit and convert ISBN-10 ↔ ISBN-13, computed locally on your device.
check digit verified
How the isbn-10 ↔ isbn-13 converter & validator works
The tool checks the ISBN's check digit, ISBN-10 uses a modulo-11 weighted sum (weights 10 down to 1, with X meaning 10), ISBN-13 uses a modulo-10 alternating 1-3 weighting. To convert an ISBN-10 to ISBN-13 it prefixes 978 and recomputes the mod-10 check digit; to go the other way it drops the 978 prefix and recomputes the mod-11 digit. Hyphens and spaces are ignored.
ISBN-13 has been the standard since 2007; older books carry ISBN-10. The 979-prefixed ISBN-13s have no ISBN-10 equivalent, so those convert one way only. This validates the check digit. It confirms the number is well-formed, not that the book exists in a catalogue.
Frequently asked questions
How do I convert ISBN-10 to ISBN-13?
Prefix the first nine digits with 978 and recompute the final check digit using the ISBN-13 (mod-10, alternating 1-3) formula. This tool does it automatically and validates the result.
What does the X in an ISBN-10 mean?
It is a check digit of 10, written as X because ISBN-10 uses modulo 11 which can produce a value of 10. It only ever appears in the last position.
Why can't my ISBN-13 convert to ISBN-10?
Only 978-prefixed ISBN-13s have an ISBN-10 equivalent. A 979 prefix has no ISBN-10, so the conversion is one-directional for those.
Does this check the book exists?
No. It validates the check digit and converts formats. It confirms the ISBN is structurally valid and not mistyped, not that it maps to a real title.
How is the ISBN-13 check digit calculated?
Multiply the first 12 digits alternately by 1 and 3, sum them, and the check digit is whatever makes that total a multiple of 10 (i.e. 10 minus the sum mod 10, or 0). For 978-0-306-40615, the weighted sum leads to a check digit of 7, giving 978-0-306-40615-7.
Can I convert an ISBN-13 back to ISBN-10?
Only if it starts with 978: drop that prefix, take the next nine digits, and recompute the mod-11 check digit (which may be X for 10). A 979-prefixed ISBN-13 has no ISBN-10 form at all, so those are 13-digit only.
How is the ISBN-10 check digit calculated?
Multiply the nine digits by weights 10 down to 2, add them, and the check digit is the value (0-10) that makes the total a multiple of 11; a value of 10 is written as X. That modulo-11 scheme is why X can appear, whereas the ISBN-13 modulo-10 digit is always 0-9.
What do the parts of an ISBN mean?
An ISBN-13 has five parts: the prefix (978 or 979), a registration-group element (language or region), the registrant (publisher), the publication element (the specific edition), and the final check digit. Hyphens separate these groups, but their positions vary, which is why this tool ignores hyphens entirely.
Is my input uploaded?
No, validation and conversion run in your browser and nothing is transmitted.