📚 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.
Is my input uploaded?
No — validation and conversion run in your browser and nothing is transmitted.