ISBN-10 / ISBN-13 Converter
Convert an ISBN between the 10 and 13 digit forms, recalculate the correct check digit for each, and see the hyphenated display form with registration group and publisher elements.
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Two numbers for the same book
Every book published since 2007 carries a thirteen digit ISBN, and every book published before then has a ten digit one. Both identify the same title, because the thirteen digit form is the ten digit form with a 978 prefix and a recomputed check digit. Library catalogues, retailer feeds, metadata exports and citation databases mix the two freely, so matching records reliably means normalising to one form.
The check digits are computed differently
ISBN-10 uses a mod-11 checksum with weights descending from ten to two, and because the result can be ten it uses the letter X for that value. ISBN-13 is a GTIN and uses the mod-10 alternating weight rule shared with EAN barcodes. That is why simply prefixing 978 and keeping the old final character produces an invalid ISBN, and it is the single most common mistake in hand converted data.
Not every ISBN-13 converts back
Only ISBN-13 numbers beginning with 978 have a ten digit equivalent, because the 979 prefix range was allocated after the ten digit format was full. A 979 ISBN has no ISBN-10 at all, and a system requiring one for those titles is working from an assumption that stopped being true years ago. The converter says so explicitly rather than producing a plausible looking number.
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Frequently Asked Questions
Why does ISBN-10 sometimes end in X?
Because its check digit is computed modulo eleven, so the valid values run from zero to ten. The value ten is written as the letter X, since it has to occupy a single character position.
Can every ISBN-13 be converted to ISBN-10?
No. Only those starting with 978. The 979 prefix was introduced when the 978 range ran out and has no ten digit equivalent, so those books have never had an ISBN-10.
Do the hyphens matter?
Not for identity; they are a display convention that separates the prefix, registration group, registrant, publication and check digit. Their positions vary by registration group and are assigned by the agency, so a stored ISBN should keep only the digits.
What does the 978 prefix mean?
It is the GS1 prefix reserved for the book trade, which is what let ISBNs become scannable retail barcodes. 979 is the second range allocated for the same purpose.
Does a valid check digit mean the book exists?
No. It means the number is well formed. Whether it was ever assigned to a published title is a question for a bibliographic database such as the ISBN agency register or a library catalogue.
Privacy & Security
Everything runs in your browser; nothing is uploaded.
How to Use
Paste an ISBN in either form to convert it and verify both check digits.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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